TEACHERS'  HANDBOOK 

TO  ACCOMPANY 

FOUNDATIONS  OF 
CHEMISTRY 


BY 

ARTHUR  A.  BLANCHARD,  PH.D. 

ASSOCIATE     PROFESSOR    OF     INORUAMC     CHEMISTRY 
AT  THE  MASSACHUSETTS   INSTITUTE  OF  TECHNOLOGY 

AND 

FRANK  B.  WADE,  B.S. 

HEAD    OF    THE    DEPARTMENT    OF    CHEMISTRY    AT    THE 
8UORTRIUGE    HIGH  9C1IOOL,   INDIANAPOLIS,    INDIANA 


AMERICAN  BOOK  COMPANY 

NEW  YORK  CINCINNATI  CHICAGO 


TEACHERS'  HANDBOOK 

TO  ACCOMPANY 

FOUNDATIONS  OF 
CHEMISTRY 


BY 

ARTHUR  A.  BLANCHARD,  PH.D. 

ASSOCIATE     PROFESSOR    OF     INORGANIC     CHEMISTRY 
AT  THE  MASSACHUSETTS   INSTITUTE  OF  TECHNOLOGY 

AND 

FRANK  B.  WADE,  B.S. 

HEAD    OF    THE    DEPARTMENT    OF    CHEMISTRY    AT    THE 
8HORTRIDGE   HIGH   SCHOOL,    INDIANAPOLIS,    INDIANA 


AMERICAN  BOOK  COMPANY 

NEW  YORK  CINCINNATI  CHICAGO 


COPYRIGHT,  1915,  BY 

ARTHUR  A.  BLANCHARD  AND 

FRANK  B.  WADE 


ALL  RIGHTS  RESERVED 


TEACHERS'  HANDBOOK 
w.  P.  i 


" 


PREFACE 

THIS"  handbook  has  been  prepared  as  a  guide  to  the  use  of  the 
authors'  textbook,  Foundations  of  Chemistry.  Although  it  is  obvious 
that  the  experienced  teacher  will  find  much  of  the  detailed  suggestion 
and  answers  to  questions  superfluous,  nevertheless  it  is  probable  that 
even  for  such  a  teacher  this  handbook  will  be  of  value  in  showing  the 
authors'  point  of  view.  Furthermore,  it  is  to  be  hoped  that  maturer 
persons,  who  may  be  studying  the  main  textbook  from  interest  in  the 
subject  and  without  the  advantage  of  class  instruction,  may  derive  a 
good  deal  of  help  from  the  use  of  the  handbook. 

The  authors  realize  that  some  matters  are  explained  very  fully  in 
the  textbook,  much  being  stated  that  might  be  left  to  the  pupils' 
imagination,  or  be  brought  out  in  classroom  discussion.  They  believe, 
however,  that  it  is  better  to  treat  few  topics  thoroughly  than  many 
superficially.  The  questions  given  at  the  end  of  each  chapter  will  be 
of  service  in  developing  the  pupils'  imagination  and  suggesting  lines 
of  class  discussion.  Furthermore,  countless  facts  and  experiences  of 
everyday  life,  of  which  the  few  treated  in  the  book  are  fairly  typical, 
may  be  studied  in  the  light  of  the  principles  developed  from  the 
selected  topics.  The  pupil  may  thus  grow  to  a  deeper  realization 
that  all  happenings  in  the  universe  occur  in  obedience  to  natural  law, 
and  that  the  more  fully  he  can  understand  the  laws  of  nature,  the 
better  he  will  be  able  to  apply  the  knowledge  he  possesses  to  the 
problems  of  his  daily  life. 

This  handbook  follows  the  order  of  the  textbook,  chapter  by  chap- 
ter. In  many  cases  it  is  suggested  that  the  teacher  use  extra  matter 
to  enrich  the  content  of  the  course  on  the  historical,  the  industrial,  or 
other  side  of  the  subject.  Trips  to  industrial  plants  are  suggested  at 
appropriate  places.  Such  trips  are  profitable  in  increasing  interest, 
in  demonstrating  the  practical  importance  of  chemistry,  and  espe- 
cially in  securing  better  acquaintance  between  pupils  and  teacher. 

33^476 


4  PREFACE 

Excursions  undertaken  in  school  time  are  usually  more  profitable 
than  those  taken  after  school  hours  or  on  Saturday. 

A  number  of  brief  quotations  from  the  original  papers  of  men  who 
have  made  great  advances  in  chemistry  have  been  given.  Some  of 
these  have  been  translated  from  the  less  accessible  originals. 

The  answers  to  most  of  the  questions  are  here  given  very  fully. 
The  authors  hold  that  monosyllabic  answers  from  the  pupils  should 
not  be  tolerated,  but  that  the  answers  should  show  an  appreciation 
of  the  purpose  of  the  question.  To  this  end  they  have  given  the 
answers  in  such  a  full  and  thoughtful  manner  as  they  would  endeavor 
to  have  their  pupils  attain.  In  many  instances  they  have  gone  be- 
yond the  knowledge  which  the  pupil  could  reasonably  be  supposed 
to  possess  in  order  to  suggest  elaborations  of  the  topic  which  could 
serve,  at  the  teacher's  discretion,  to  make  the  classroom  work  of  more 
value.  In  the  solution  of  the  numerical  problems  possibly  an  excess 
of  detail  in  the  steps  of  the  process  is  given,  but  the  authors  believe 
it  is  better  to  err  on  this  side.  The  mere  numerical  correctness  of  the 
answer  from  the  pupil  is  of  secondary  importance  to  the  understand- 
ing of  the  application  to  the  problem,  of  scientific  principles. 

If  experiments  precede  the  classroom  and  textbook  work  and 
embody  in  part  at  least  the  spirit  of  the  discovery  method,  if  class- 
room discussion  follows,  and  lastly,  if  the  use  of  the  textbook  sup- 
plements and  arranges  the  material  in  orderly  fashion,  it  is  believed 
that  good  results  will  be  obtained. 


TEACHERS'    HANDBOOK 


CHAPTER  I 

CHEMICAL  AND  PHYSICAL  CHANGES 

Pages  9-14 

As  a  first  experiment  in  chemistry  to  give  a  concrete  illustration 
of  the  nature  of  chemical  change,  something  likely  to  be  of  intense 
interest  to  the  pupil  should  be  selected.  The  material  used  should 
be  familiar  to  the  pupil.  We  would  suggest  the  lighting  of  a  small 
pinch  of  black  gunpowder  placed  on  a  piece  of  paper.  This  will 
show  the  principal  features  of  chemical  change  and  at  the  same 
time  awaken  interest  in  the  pupils.  The  evolution  of  heat  and 
light  are  obvious.  The  new  products  formed  are  easily  seen  and 
smelled,  both  those  that  are  scattered  in  the  smoke  and  those  that 
remain  on  the  paper.  A  word  about  the  objectionable  character 
of  smoke  from  black  gunpowder  when  used  in  war,  and  a  hint  to 
the  effect  that  smokeless  powder  produces  only  invisible  gases  as 
new  products,  may  add  to  the  interest. 

A  physical  change  can  be  illustrated  by  melting  a  bit  of  ice,  boil- 
ing the  water  thus  obtained,  condensing  some  of  the  steam  on  the 
under  side  of  a  watch  glass,  and  freezing  the  dew  thus  formed  by 
rapidly  evaporating  ether  in  the  watch  glass.  Use  a  current  of  air 
to  assist  the  evaporation  of  the  ether. 

Answers  to  Questions  on  Chapter  I 

Page  14 

1.  Different  chemical  substances  are  distinguished  by  their 
different  properties.  Physical  properties  are  evident  to  us  through 
our  senses  of  sight,  feeling,  smell,  taste,  and  hearing.  Chemical 


6  CHEMICAL  AND   PHYSICAL   CHANGES 

properties  are  shown  in  the  ability  of  substances  to  undergo  chemi- 
cal change,  the  latter  always  being  accompanied  by  changes  of 
physical  properties. 

2.  Chemical  changes  differ  from  physical  changes  hi  the  follow- 
ing respects : 

(1)  A  chemical  change  involves  a  complete  change  of  properties, 
that  is,  the  disappearance  of  the  properties  of  the  substance  or 
substances  entering  the  change,  and  the  appearance  of  new  prop- 
erties which  are  the  properties  of  the  substance  or  substances  pro- 
duced in  the  change. 

Physical  changes  do  not  involve  a  complete  change  of  properties. 
The  changes  are  caused  by  the  application  of  some  physical  force, 
and  when  the  force  is  removed  the  substances  are  free  to  return  to 
their  original  condition. 

(2)  Chemical  changes  are  accompanied  by  a  heat  effect,  often  a 
very  marked  one  accompanied  by  the  evolution  of  light.     Physical 
changes  do  not  necessarily  involve  any  heat  effect. 

(3)  Another  distinction  was  hinted  at  in  the  statement  on  page 
11  that  the  carbon  dioxide  produced  by  burning  charcoal  weighs 
3f  times  as  much  as  the  charcoal.     This  statement  in  connection 
with  the  law  of  the  conservation  of  matter  shows  that  the  same 
definite  proportion  must  always  exist  between  the  weights  of  the 
substances  entering  this  chemical  change.     If  two  substances  are 
mixed  physically,  for  example  sugar  and  sand,  they  may  be  mixed 
in  any  proportion. 

3.  Five  examples  of  physical  change  are: 

(1)  Crushing  of  rock  in  a  stone  crusher. 

(2)  Hammering  of  gold  into  gold  leaf. 

(3)  Compressing  air  in  an  automobile  tire. 

(4)  Careful  mixing  together  of  powdered  charcoal,   powdered 
sulphur,  and  powdered  saltpeter,  in  making  the  mixture  called 
gunpowder. 

(5)  The  shortening  of  a  steel  rail  on  a  cold  day  and  its  lengthen- 
ing on  a  hot  day. 

4.  Five  instances  of  chemical  change  and  points  that  distinguish 
them  from  physical  changes  are : 

(1)  Sugar  is  scorched  during  cooking:    The  new  properties  of  a 


PAGES  9-14  7 

brown  or  black  color  and  a  burnt  taste  appear  and  remain  perma- 
nently even  after  the  sugar  has  cooled  to  ordinary  temperature. 

(2)  Bleaching  of  cloth :    The  property  of  color  is  changed,  indi- 
cating that  some  highly  colored  substance  in  the  cloth  is  changed 
chemically. 

(3)  Ripening  of  fruit :   Unripe  fruit  tastes  sour  ;•  ripe  fruit  tastes 
sweet,  indicating  that  a  sour  substance  has  disappeared  in  the  form- 
ing of  a  sweet  substance. 

(4)  Explosion  of  gunpowder:    Heat  and  light  are  produced.     A 
large  quantity  of  gases  is  formed,  and  the  solid  substance  left  bears 
no  resemblance  to  the  original  gunpowder. 

(5)  The  spoiling  of  eggs :    During  this  process  the  eggs  acquire 
a  very  offensive  odor,  a  new  property  which  indicates  the  formation 
of  a  new  substance. 

5.  Three  instances  of  chemical  change  in  which  the  heat  effect 
is  so  intense  as  to  cause  the  emission  of  light : 

(1)  Burning  of  wood. 

(2)  Explosion  of  gunpowder. 

(3)  Explosion  of  photographic  flash-light  powder. 

6.  Three  instances  of  chemical  change  in  which  the  heat  effect  is 
noticeable,  but  not  so  intense  as  to  cause  emission  of  light: 

(1)  Slow  combustion  of  food  materials  within  the  body. 

(2)  Fermenting  of  a  manure  pile. 

(3)  The  action  which  results  from  mixing  lime  and  water. 

7.  Three  instances  of  chemical  change  in  which  the  heat  effect  is 
not  noticeable : 

(1)  Rusting  of  iron. 

(2)  Ripening  of  fruit. 

(3)  The  tarnishing  of  silver,  as  when  a  silver  spoon  is  used  in 
eating  an  egg. 

8.  A  substance  hotter  than  its  surroundings  cools  off  more  or 
less  rapidly  because  the  heat  escapes  into  the  surroundings.     When 
wood  burns,  so  much  heat  is  produced  within  a  short  time  by  the 
chemical  change  that  it  cannot  all  escape  at  once.     Therefore  the 
heat  becomes  very  intense  within  the  body  of  wood  and  amid  the 
gases  of  the  flame.     If  the  same  amount  of  wood  decays  completely, 
the  same  amount  of  heat  is  produced,  but  so  slowly  that  it  can  escape 


8  MIXTURES  AND   CHEMICAL  SUBSTANCES 

just  about  as  rapidly  as  it  is  produced,  hence  the  heat  within  the 
body  of  wood  cannot  become  much  more  intense  than  in  the  sur- 
roundings. 

9.  The  material  products  of  burning  coal  in  a  furnace  are  gases 
which  pass  up  the  chimney ;  smoke,  which  consists  of  solid  particles 
and  globules  of  tarry  matter ;  and  ashes,  which  consist  of  the  incom- 
bustible residue  from  the  coal.     These  products  are  of  no  use,  and  the 
ashes  and  smoke  are  difficult  to  dispose  of  without  making  a  nui- 
sance.    Hence  the  furnace  is  surely  not  run  to  obtain  these  sub- 
stances. 

10.  After  a  mason  slakes  lime,  he  allows  the  product  to  cool 
before  he  uses  it  mixed  with  sand  and  hair  as  mortar.     In  this  reac- 
tion it  is  the  material  product  and  not  the  heat  that  is  sought. 


CHAPTER   II 

MIXTURES    AND    CHEMICAL    SUBSTANCES 

Pages  15-19 

To  illustrate  the  separation  of  a  mechanical  mixture  it  may  be 
well  to  have  the  pupils  separate  the  constituents  of  black  gunpowder, 
with  which  they  are  already  familiar.  To  do  this  treat  a  pinch  of 
powder  with  a  few  c.c.  of  carbon  disulphide,  filter  into  a  watch 
glass,  and  allow  the  disulphide  to  evaporate.  This  will  give  sulphur 
by  itself.  Next  use  a  few  c.c.  of  water  with  the  solid  residue  (first 
allow  all  the  carbon  disulphide  to  evaporate)  and  again  filter  on  to 
a  clean  watch  glass.  On  evaporating  the  water,  they  will  now  ob- 
tain saltpeter.  The  insoluble  charcoal  of  the  gunpowder  will  be 
left  on  the  filter  paper.  As  gunpowder  is  so  excellently  blended,  few 
pupils  would  suspect  at  first  that  it  is  a  mixture,  and  yet  the  simple 
physical  means  of  separation  above  outlined  will  serve  to  show  its 
character. 


PAGES  15-19  9 

Answers  to  Questions  on  Chapter  II 

Page  19 

1.  Matter  is  that  of  which  any  physical  object  or  body  is  com- 
posed, whatever  its  form  or  condition,  whether  gaseous  like  air, 
liquid  like  water,  or  solid  like  stone.     Anything  which  possesses 
mass  is  matter.     In  physics,  the  mass  of  a  body  of  matter  is  measured 
by  the  force  necessary  to  set  the  body  in  motion,  or  to  bring  the  body 
to  rest  if  it  is  already  in  motion.     The  mass-of  a  body  is  more  con- 
veniently measured  by  its  weight,  that  is,  by  the  force  with  which  it 
is  attracted  to  the  earth.     Therefore  matter  is  anything  which  pos- 
sesses mass  or  weight. 

Substance  in  its  most  general  meaning  is  almost  synonymous  with 
matter.  Anything  which  has  substance  is  matter.  A  substance  is, 
however,  usually  understood  to  be  a  particular  kind  of  matter. 

A  mixture  consists  of  more  than  one  kind  of  matter,  that  is,  of  more 
than  a  single  substance.  In  its  popular  use,  however,  the  term 
substance  is  often  applied  to  mixtures. 

A  body  is  a  mass  of  matter  considered  separately  from  other 
matter. 

An  object  is  a  material  thing  of  definite  size  and  shape. 

2.  The  word  substance  in  its  popular  meaning  may  be  applied  to 
anything  which  is  composed  of  matter,  although  it  usually  implies 
matter  having  special  characteristics  which  readily  distinguish  it 
from  other  sorts  of  matter.     In  science,  a  pure  substance  is  a  definite 
kind  of  matter  unmixed  with  other  kinds  of  matter.     Popularly 
gravel,  garden  soil,  mortar,  paper,  wood,  gunpowder,  baking  powder, 
coffee,  leather,  blood,  flesh,  etc.,  would  be  classed  as  substances, 
although  chemically  each  of  these  is  a  mixture  of  several  substances. 
The  word  material  could  properly  be  used  in  describing  each  of 
these  mixtures. 

3.  Rain  water  is  a  pure  substance.     It  is  exactly  the  same  sub- 
stance as  pure  water  which  comes  from  any  other  source  than  the 
clouds. 

Sea  water  is  a  mixture  of  water  with  small  amounts  of  several 
other  substances. 

The  Atlantic  Ocean  is  a  body  of  sea  water. 


10  ELEMENTS  AND  COMPOUNDS 

Lake  Superior  is  a  body  of  water.  Although  the  water  of  the  lake 
is  not  absolutely  free  from  other  substances,  it  may  in  comparison 
with  ocean  water  be  classed  as  a  pure  substance. 

The  block  of  ice  is  a  body  composed  of  a  practically  pure  substance. 

Sugar  is  a  substance. 

Mapk  sugar  would  popularly  be  classed  as  a  substance.  Scientifi- 
cally, it  is  composed  of  the  substance  sugar  mixed  with  small  quan- 
tities of  natural  coloring  and  flavoring  substances. 

Hash  is  a  mixture.    - 

A  mince  pie  is  an  object  formed  from  various  materials,  most  of 
which  are  mixtures. 

The  marble  statue  is  an  object  composed  of  a  nearly  pure  substance. 

The  ledge  of  marble  is  a  body  consisting  in  the  main  of  marble, 
although  it  is  certain  to  contain  much  more  foreign  matter  than  the 
carefully  selected  block  chosen  for  the  statue. 

Iron  is  a  substance,  although  practically  all  of  what  is  ordinarily 
called  iron  contains  a  small  amount  of  other  chemical  substances 
than  iron. 

The  old  cannon  is  an  object  composed  of  iron. 

4.  By  agitating  a  mixture  of  iron  filings  and  powdered  sulphur 
near  a  magnet,  one  allows  the  particles  of  iron  to  be  drawn  to  the 
magnet  while  the  sulphur  is  left  behind. 

6.  A  mixture  of  salt  and  sand  may  be  stirred  with  water,  where- 
upon the  salt  dissolves.  The  solution  may  be  drained  off  from  the 
sand  and  then,  when  the  water  is  evaporated,  dry  salt  is  left. 


CHAPTER  III 

ELEMENTS   AND    COMPOUNDS 

Pages  20-24 

IT  will  be  well  in  connection  with  this  chapter  to  let  the  pupil 
actually  perform  the  experiment  with  iron  filings  and  sulphur  which 
is  described  in  the  text.  Most  laboratory  manuals  give  detailed 
instructions  for  this  experiment.  The  separation  of  the  experiment 
into  parts  is  advisable  with  beginners.  Let  them  first  study  the 


PAGES  20-24  11 

mixture  and  separate  the  iron  from  the  sulphur  by  various  means, 
thus  showing  that  no  new  substance  results  on  merely  mixing  iron 
and  sulphur.  Then  let  them  heat  the  mixture  and  study  the  residue 
as  a  separate  experiment.  There  is  then  less  likelihood  of  their  be- 
coming confused  as  to  what  they  are  trying  to  prove. 

Answers  to  Questions  on  Chapter  III 
Page  24 

1.  An  elementary  substance  is  a  pure  substance  which  cannot  be 
decomposed  chemically  into  other  substances. 

A  compound  is  a  pure  substance  composed  of  two  or  more  elements. 

An  element  is  one  of  the  eighty-three  constituents  of  all  known 
kinds  of  matter.  An  element  by  itself,  that  is,  when  not  in  combina- 
tion with  other  elements,  has  definite  properties  by  which  it  is 
recognized  as  a  definite  substance.  The  physical  properties  of  the 
element  are  completely  changed  when,  through  chemical  combina- 
tion with  other  elements,  it  becomes  a  constituent  of  new  sub- 
stances. The  element  itself,  however,  still  exists,  for  it  can  always 
be  separated  by  chemical  means  from  the  compound  and  obtained 
again  undiminished  in  weight  and  exhibiting  its  original  properties 
in  every  particular.  The  identity  of  the  element  then  is  not  altered 
through  chemical  change,  but  the  identity  of  the  elementary  sub- 
stance is  lost. 

2.  For  a  list  of  elements  see  inside  back  cover  of  Foundations  of 
Chemistry. 

3.  Salt,  sugar,  water,  glass,  and  marble  are  compounds. 

4.  We  cannot  hope  ever  to  be  able  to  convert  lead  into  gold,  for, 
as  a  result  of  all  the  most  painstaking  experiments  since  chemistry 
has  been  studied  as  a  science,  it  can  be  asserted  that  in  no  chemical 
change  is  there  an  increase  or  decrease  in  the  weight  of  any  element 
concerned  large  enough  to  be  detected  with  the  chemical  balance. 

It  is  true  that  recent  discoveries  concerning  radium,  niton,  and  a 
few  other  elements  have  indicated  very  clearly  that  the  elements 
are  really  complex  and  that  some  at  least  are  constantly  changing 
over  into  others.  Yet  the  amounts  involved  in  such  changes  are  un- 
weighably  small,  and  furthermore  no  force  which  human  ingenuity 


12  COMBUSTION 

has  yet  been  able  to  bring  to  bear  has  had  any  effect  in  hastening  or 
retarding  such  changes. 

We  can  therefore  regard  the  mass  of  gold  and  that  of  lead  in  our 
earth  as  constant,  at  least  for  any  period  of  time  which  will  come 
within  the  limits  of  human  observation.  It  has  been  found  that 
radium  is  slowly  but  constantly  changing  into  niton,  but  no  indica- 
tion has  ever  been  discovered  that  lead  is  changing  into  gold.  Yet 
it  is  perfectly  possible  that  such  a  change  is  taking  place,  only  in- 
finitely slowly.  No  one  would  be  rash  enough  to-day  to  assert  that 
no  force  will  ever  be  discovered  which  will  hasten  this  change  so  that 
one  will  be  able  to  see  lead  change  into  gold  while  he  waits.  But 
such  a  possibility  is  so  contrary  to  all  our  experiences  that  we  have  no 
ground  for  hoping  for  its  fulfillment. 

5.   See  Law  of  Definite  Proportions,  Section  11,  page  22. 

CHAPTER   IV 

COMBUSTION 

Pages  25-37 

IN  this  chapter  we  have  a  subject  which  is  of  the  greatest  inter- 
est to  the  chemist,  as  it  was  largely  through  the  progress  made  in 
the  knowledge  of  the  true  nature  of  combustion  that  modern  chemis- 
try got  its  start.  The  lack  of  a  true  understanding  of  the  problem 
on  the  part  of  Priestley,  who  discovered  oxygen,  yet  never  clearly 
understood  the  part  it  plays  in  combustion,  should  be  pointed  out 
to  the  class.  Lavoisier's  splendid  demonstration  of  the  nature  of 
combustion  should  also  receive  attention.  The  phlogiston  theory 
should  be  clearly  presented,  and  it  should  be  shown  how  natural 
was  the  error  of  those  who  believed  in  it,  since  the  products  of  ordi- 
nary combustion  are  so  often  gaseous. 

The  early  discovery  of  the  increase  in  weight  of  metals  when  heated 
in  air  should  be  brought  out.  In  this  connection  the  following  quo- 
tation from  the  original  paper  of  Jean  Rey  (1630)  l  may  well  be  read 

1  Rey,  Jean,  Essays  on  an  Inquiry  into  the  Cause  wherefore  Tin  and  Lead 
Increase  in  Weight  on  Calcination.  Alembic  Club  Reprint,  No.  11,  page  36, 
Edinburgh. 


PAGES  25-37  13 

to  the  class  to  show  them  that  Rey  was  far  ahead  of  his  time  and  got 
no  recognition  from  his  contemporaries,  who  still  continued  to  be- 
lieve in  the  phlogiston  theory  for  over  a  hundred  years. 

"  Now  I  have  made  the  preparations,  nay,  laid  the  foundations 
for  my  answer  to  the  question  of  the  Sieur  Brun,  which  is,  that  hav- 
ing placed  two  pounds  six  ounces  of  fine  English  tin  in  an  iron  vessel 
and  heated  it  strongly  on  an  open  furnace  for  the  space  of  six 
hours  with  continual  agitation  and  without  adding  anything  to  it,  he 
recovered  two  pounds  thirteen  ounces  of  a  white  calx ;  which  filled 
him  first  with  amazement,  and  with  a  desire  to  know  whence  the 
seven  ounces  of  surplus  had  come.  ...  To  this  question,  then, 
I  respond  and  sustain  proudly,  resting  on  the  foundations  already 
laid,  '  That  this  increase  in  weight  comes  from  the  air,  which  in  the 
vessel  has  been  rendered  denser,  heavier,  and  in  some  measure  adhe- 
sive by  the  vehement  and  long- continued  heat  of  the  furnace; 
which  air  mixes  with  the  calx  (frequent  agitation  aiding)  and  be- 
comes attached  to  its  most  minute  particles;  not  otherwise  than 
water  makes  heavier  sand  which  you  throw  into  it  and  agitate,  by 
moistening  it  and  adhering  to  the  smallest  of  its  grains.' " 

Another  original  paper  which  will  be  of  interest  to  pupils  in  con- 
nection with  the  subject  of  combustion  is  Priestley's  paper  on 
his  discovery  of  oxygen.1  After  telling  of  his  becoming  possessed 
of  a  12-inch  burning  lens,  Priestley  says,  "  With  this  apparatus, 
on  the  1st  of  August,  1774,  I  endeavored  to  extract  air  from  mer- 
curius  calcinatus  (red  oxide  of  mercury) ;  and  I  presently  found  that 
by  means  of  this  lens  air  was  expelled  from  it  very  readily.  Having 
got  about  three  or  four  times  as  much  as  the  bulk  of  my  materials, 
I  admitted  water  to  it,  and  found  that  it  was  not  imbibed  by  it. 
But  what  surprised  me  more  than  I  can  well  express,  was  that  a 
candle  burned  in  this  air  with  a  remarkably  vigorous  flame,  and  a 
piece  of  red-hot  wood  sparkled  in  it,  exactly  like  paper  dipped  in  a 
solution  of  niter,  and  it  consumed  very  fast."  He  says  also  that 
while  hi  Paris,  "  I  frequently  mentioned  my  surprise  at  the  kind  of 
air  which  I  had  got  from  this  preparation  to  Mr.  Lavoisier,  Mr. 
le  Roy,  and  several  other  philosophers,  who  honored  me  with  their 

1  Quotation  from  Alembic  Club  Reprints,  No.  7,  page  8. 


14  COMBUSTION 

notice  in  that  city ;  and  who  I  dare  say  cannot  fail  to  recollect  the 
circumstance." 

In  this  connection  call  attention  to  the  fact  that  it  was  this  same 
"  Mr.  Lavoisier  "  who  finally  made  use  of  Priestley's  discovery 
to  straighten  out  the  problem  of  the  true  nature  of  combustion. 

In  connection  with  the  study  of  the  action  of  air  on  metals,  it 
will  be  well  to  have  all  pupils  heat  bits  of  each  of  several  common  metals 
in  the  Bunsen  flame.  Iron  and  copper  should  of  course  be  used 
by  all.  Magnesium  may  be  used  either  by  the  instructor  or,  if 
plenty  is  at  hand,  by  all  pupils,  to  illustrate  the  case  of  a  very  active 
metal.  In  this  connection  some  thermit;  the  well-known  Gold- 
schmidt  mixture  of  iron  oxide  and  aluminium  powder,  may  perhaps 
be  used  by  the  teacher.  The  iron  oxide  in  it  can  be  shown  to  be  the 
same  as  the  scale  that  the  pupils  get  from  the  iron  that  they  heat 
in  air.  Thus  they  may  be  shown  how  oxygen  may  be  stored  in  com- 
bination and  used  later  even  more  effectively  than  when  in  the  free 
state.  The  term  oxidizing  agent  may  be  introduced  here  for  later 
use. 

Bits  of  pure  gold,  silver,  and  platinum  might  well  be  heated  by 
pupils  or  teacher  to  show  the  lack  of  activity  of  the  precious  metals 
toward  oxygen. 

Class  discussion  of  the  bearing  of  the  facts  learned  in  the  above 
work  on  the  practical  uses  of  the  several  metals  will  be  valuable. 
Tin  roofs,  copper  roofs,  the  use  of  sheet  lead  and  galvanized  iron, 
and  the  use  of  the  precious  metals  in  jewelry  may  be  mentioned. 

A  classroom  demonstration  of  the  gain  in  weight  when  the  prod- 
ucts of  combustion  of  a  candle  are  caught,  weighed,  and  compared 
with  the  weight  of  the  candle,  is  always  of  great  interest  to  classes. 
The  gain  in  weight  of  an  oxidizing  metal  may  well  be  proved  by  each 
pupil.  For  this  purpose  magnesium  ribbon  heated  in  a  tared  cruci- 
ble serves  admirably  because  of  the  rapidity  of  the  action  and  the 
marked  gain  in  weight.  If  it  is  thought  advisable  to  take  the  time 
for  it,  a  comparison  of  the  per  cent  gain  of  weight  obtained  by  dif- 
ferent members  of  the  class  will  illustrate  roughly  the  definiteness  of 
the  proportions  by  weight  existing  between  the  metal  and  the  oxygen 
which  joins  it.  This  example  of  definite  combining  proportions  will 
be  found  valuable  for  reference  on  many  later  occasions. 


PAGES  25-37  15 

With  the  first  quantitative  experiment  performed  by  the  pupils 
some  little  time  will  of  course  have  to  be  taken  in  explanation  of  the 
proper  use  and  care  of  the  balance.  The  metric  system  should  also 
receive  some  attention  at  this  time.  Pupils  frequently  find  difficulty 
in  understanding  the  denominations  of  weights,  especially  the  frac- 
tional parts  of  the  gram. 

If  the  box  of  weights  is  likened  to  a  merchant's  cash  drawer  and 
the  weights  themselves  to  pieces  of  money  (i.e.  50 i  piece,  20  i  piece, 
10?f  piece,  §i  piece,  2^  piece,  and  \i  piece)  pupils  will  readily  learn  the 
denomination  of  each  weight  from  their  familiarity  with  United 
States  money.  The  counting  of  weights  will  then  become  as  simple 
a  matter  as  counting  money. 

For  the  sake  of  the  training  in  manipulation  and  in  carefulness,  it 
will  pay  to  teach  and  to  insist  upon  as  careful  handling  of  the  bal- 
ance as  though  it  had  the  accuracy  of  a  fairly  good  chemical  bal- 
ance. Few  schools  will  have  for  the  use  of  pupils  balances  that  are 
accurate  beyond  the  second  decimal  place,  and  pupils  should  not  be 
held  for  results  beyond  the  possibility  of  their  apparatus. 

Where  more  than  one  or  two  balances  are  available,  it  will  be 
found  advantageous  to  assign  each  pupil  to  a  definite  balance  and  to 
hold  pupils  responsible  for  the  loss  of  weights  or  for  damage  to  the 
balance.  By  thus  assessing  minor  losses  against  the  pupils,  the 
laboratory  can  afford  to  use  more  costly  balances  and  to  keep  them 
in  repair. 

For  the  sake  of  frequent  subsequent  reference,  it  will  be  found 
valuable  to  point  out  clearly  to  the  pupils  the  origin  of  the  gram. 
The  fact  that  it  is  the  weight  of  1  c.c.  of  water  (at  4  degrees  C.,  to  be 
exact)  becomes  useful  later  in  calculating  the  volumes  of  liquids 
from  the  weight  in  grams  and  the  specific  gravity. 

In  connection  with  the  discussion  of  slow  combustion  in  the 
body  (Section  26)  a  little  outline  of  the  physiology  of  respiration  will 
be  valuable  to  the  pupils,  as  many  of  them  will  not  have  had  it  in 
other  courses,  and  others  may  later  take  physiology  and  thus  have 
a  bit  of  foundation  laid  for  that  work.  The  matter  of  proper  ven- 
tilation may  be  touched  upon  here,  and  the  fact  that  it  is  not  the 
presence  of  carbon  dioxide  that  makes  the  air  of  a  room  unsuitable 
in  most  cases  should  be  brought  out.  Overheating,  with  too  much  or 


16  COMBUSTION 

with  too  little  moisture  present,  may  be  mentioned  as  more  probable 
causes  of  discomfort  in  such  cases. 

The  topic  of  smoke  prevention  (Section  28,  p.  33)  is  one  of  vast 
social  significance,  and,  especially  in  the  soft  coal  burning  sections  of 
the  country,  is  deserving  of  considerable  attention  in  the  chemistry 
course.  The  principles  back  of  complete  combustion  can  easily  be 
given  at  this  time,  and  a  visit  to  some  progressive  plant  which  is 
equipped  with  proper  smoke-preventing  devices  should  by  all  means 
be  made.  If  it  can  be  done  in  class  time  so  that  all  pupils  can  go, 
so  much  the  better.  It  will  be  worth  more  than  the  same  amount 
of  time  spent  in  school.  It  will  be  necessary  for  the  teacher  to  ex- 
plain the  nature  of  destructive  distillation  and  perhaps  actually 
heat  some  soft  coal  in  a  test  tube  to  put  clearly  before  the  pupil 
the  principal  cause  of  the  formation  of  smoke.  The  procuring 
and  maintaining  of  a  temperature  sufficiently  high  to  kindle  the 
smoke  before  it  reaches  the  comparatively  cold  surfaces  of  the  boiler, 
and  the  supplying  of  sufficient  (but  not  excessive)  air  to  unite  with 
the  smoke  complete  the  chief  requisites  for  complete  combustion. 

Answers  to  Questions  on  Chapter  IV 
Page  36 

1.  The  strongest  proof  that  something  from  the  air  is  concerned 
in  combustion  lies  in  the  fact  that  by  allowing  metals  to  act  on  a 
confined  volume  of  air,  the  volume,  as  well  as  the  weight,  of  the  air 
diminishes.  Metals  like  lead,  iron,  zinc,  copper,  and  mercury 
thus  lessen  the  volume  of  air  if  they  are  heated  in  it.  Moist  iron 
filings  act  in  this  way  fairly  rapidly  even  at  ordinary  temperature. 
Air  which  has  thus  been  deprived  of  a  part  of  its  substance  is  no 
longer  capable  of  causing  the  corrosion  of  metals  or  of  supporting 
the  active  combustion  of  substances  like  wood  and  charcoal. 

Although  the  phlogistic  chemists  explained  the  gain  in  weight  of 
metals  when  they  changed  to  calces  by  the  assumption  that  the 
phlogiston  which  escaped  had  a  negative  weight,  their  viewpoint 
becomes  almost  impossible  to  uphold  when  we  consider  the  fact 
that  the  air  into  which  the  phlogiston  is  supposed  to  be  escaping 
loses  in  volume  as  well  as  in  weight. 


PAGES  25-37  17 

2.  Iron  rust  is  porous  and  allows  air  to  penetrate  through  to  the 
metal  underneath  so  that  a  piece  of  iron  may  in  time  become  rusted 
completely  through.     On  the  other  hand,  the  coatings  formed  by 
oxidation  on  the  surface  of  copper,  zinc,  and  lead  are  impervious  and 
protect  the  metal  underneath  from  further  action  of  the  air. 

3.  The  paint  used  on  iron  bridges  is  impervious  to  the  atmos- 
phere and  thus  prevents  corrosion.     The  film  of  oxide  (or  basic  car- 
bonate) which  rapidly  forms  over  the  surface  of  copper  exposed  to 
the  atmosphere  renders  the  use  of  paint  unnecessary. 

4.  In  charcoal  fires  there  are  invariably  parts  in  the  interior 
of  the  incandescent  mass  where  the  amount  of  oxygen  is  deficient  and 
carbon  monoxide  is  therefore  formed.     This  is  very  apt  to  escape 
and  become  cooled  to  below  the  kindling  temperature,  before  it 
comes  in  contact  with  sufficient  oxygen  to  burn  it  to  carbon  dioxide. 

On  the  other  hand,  a  plentiful  air  supply  has  access  to  the  hot 
gas  flame  from  all  sides,  and  although  carbon  monoxide  probably 
exists  in  the  interior  of  all  such  flames  (in  fact  illuminating  gas 
often  contains  a  large  proportion  of  carbon  monoxide),  it  is  impos- 
sible for  it  to  get  beyond  the  very  hot  part  of  the  flame  before  it  is 
completely  burned. 

5.  The  facts  that  the  animal  body  is  continually  giving  off  heat 
and  that  carbon  dioxide  can  be  shown  to  be  exhaled  from  the  lungs 
prove  that  combustion  is  taking  place  within  the  body. 

6.  The  rapid  breathing  of  the  runner  and  the  use  of  the  black- 
smith's bellows  both  supply  a  greater  amount  of  oxygen,  making 
more  rapid  oxidation  possible. 

7.  Smoke  consists  of  carbon  and  tarry  matter.     If  these  are 
burned,  more  heat  is  produced  than  if  the  smoke  passes  unburned 
up  the  chimney. 

8.  If  we  rake  a  lot  of  fresh  leaves  on  top  of  a  burning  pile,  the 
heat  of  the  fire  underneath  decomposes  the  leaves,  and  some  of  the 
products  of  decomposition  escape  as  smoke.     This  smoke  consists 
largely  of  tarry  matter  which  is  combustible  but  is  below  its  kindling 
temperature.     When  the  layer  of  leaves  is  heated  enough  so  that 
the  flame  can  break  through  from  below  without  being  chilled,  the 
nearest  part  of  the  smoke  is  raised  to  its  kindling  temperature,  the 
combustion  of  the  smoke  particles  produces  the  heat  necessary  to 


18  COMBUSTION 

raise  the  temperature  of  the  surrounding  smoke  particles  to  their 
kindling  temperature,  and  so  all  of  the  smoke  is  consumed  and  its 
escape  seems  to  cease  as  if  by  magic. 

9.  Soft  coal  is  similar  to  leaves  in  that  heat  decomposes  it  into 
tarry  matter  and  soot  which  pass  off  as  smoke  unless  they  are  able  to 
burn.     If  a  stoker  throws  a  large  quantity  of  soft  coal  on  a  fire  in  a 
furnace,  the  surface  is  chilled  and  the  decomposition  products  there- 
fore escape  as  smoke  until  the  layer  of  fresh  coal  is  heated  through 
so  that  the  smoke  is  heated  to  its  kindling  temperature.     Of  course 
even  then  smoke  may  continue  to  escape,  if  sufficient  air  for  com- 
plete combustion  is  not  admitted  to  the  space  above  the  fire. 

By  shoveling  in  small  amounts  of  coal  frequently,  but  at  no  time 
enough  to  chill  any  large  part  of  the  surface  of  the  fire,  and  by  care- 
fully adjusting  the  drafts  into  the  combustion  chamber,  a  stoker 
can  almost  eliminate  smoke  even  from  the  ordinary  furnace. 

The  design  and  manipulation  of  a  furnace  so  as  to  prevent  smoke 
are  discussed  in  Section  28,  p.  33. 

10.  The  steaming  of  a  pile  of  manure  in  winter  indicates  heat 
within  the  pile.     This  heat  can  be  produced  only  by  some  chemical 
reaction  which  is  probably  in  the  nature  of  a  slow  combustion  simi- 
lar to  the  decay  of  wood.     This  reaction,  to  produce  so  marked  a 
steaming,  must  be  considerably  more  rapid  than  the  decay  of  wood. 

11.  A  camper  blows  his  fire  when  it  gets  low  for  the  same  reason 
that  a  blacksmith  uses  his  bellows  when  he  wishes  a  more  intense  heat. 

One  might  ask  why  blowing  extinguishes  a  candle  or  a  match  in- 
stead of  making  it  burn  brighter  in  consequence  of  the  increased 
supply  of  oxygen.  The  answer  to  this  is  that  the  candle  or  match 
as  it  ordinarily  burns  has  ample  oxygen  supplied  to  burn  the  mate- 
rial as  rapidly  as  it  can  be  raised  to  its  kindling  temperature  by  the 
heat  of  the  flame.  Blowing  forces  the  flame,  that  is  the  source  of 
heat,  away  from  the  object  which  requires  the  heat.  Furthermore 
the  added  amount  of  cold  air  cools  the  object,  which  then  falls  to  be- 
low its  kindling  temperature. 

12.  The  principal  service  of  water  in  extinguishing  a  fire  is  that 
it  cools  the  burning  materials  below  their  kindling  temperatures. 
The  exclusion  of  oxygen  by  the  water,  and  more  particularly  by  the 
steam  formed  from  it,  also  plays  a  part. 


PAGES  38^19  19 

CHAPTER  V 

OXYGEN 

Pages  38-49 

IN  connection  with  the  preparation  of  oxygen  a  modification  of 
the  historic  experiment  of  Priestley  may  well  be  given.  By  using 
small  closed  tubes  prepared  by  the  pupils  themselves  from  ordinary 
small  glass  tubing,  only  a  small  amount  of  the  relatively  costly 
mercuric  oxide  need  be  used.  The  Bunsen  burner  will  of  course 
take  the  place  of  Priestley's  burning  glass. 

By  the  use  of  leading  questions,  the  pupils  can  be  brought  to 
reason  out  for  themselves  that  the  same  gas  which  causes  mercury 
to  become  covered  with  a  red  powder  when  heated  in  air  also  causes  a 
pine  splint  to  burn.  Although  the  mercuric  oxide  used  to-day  is  prob- 
ably never  made  by  direct  oxidation  of  mercury,  it  may  be  explained 
that  the  same  product  might  be  thus  obtained,  and  by  heating  this 
product  a  gas  is  given  off  which  does  support  ordinary  combustion. 

The  teacher  cannot  be  too  careful  in  connection  with  the  use  of 
potassium  chlorate  for  the  preparation  of  oxygen,  as  it  makes  a  vio- 
lently explosive  mixture  with  almost  any  combustible  substance. 
Such  mixtures  frequently  detonate  on  slight  friction.  Hence  every 
precaution  should  be  taken  to  see  that  the  pupils  do  not  obtain  any 
quantity  of  the  material,  or  use  what  is  given  to  them  except  as 
directed.  It  is  probably  not  advisable  to  tell  them  of  the  possibili- 
ties, but  rather  repeat  the  caution,  doubtless  already  many  times 
repeated,  that  they  attempt  nothing  without  specific  direction  from 
the  teacher.  The  manganese  dioxide  used  should  first  be  tested  by 
the  teacher  by  heating  a  small  sample  with  potassium  chlorate  in  a 
test  tube,  and  if  any  considerable  amount  of  combustion  is  in  evi- 
dence, the  manganese  dioxide  should  not  be  used  for  this  purpose. 
Granular  manganese  dioxide  is  more  likely  to  be  free  from  carbon  or 
other  impurity  than  the  powdered  form,  and  having  less  surface  it 
will  not  cause  as  rapid  evolution  of  oxygen  from  the  potassium  chlo- 
rate. This  is  a  real  advantage  in  this  case,  as  pupils  frequently 
fail  to  collect  the  oxygen  as  fast  as  it  is  evolved. 


20  OXYGEN 

For  the  preparation  of  oxygen  on  the  lecture  table  the  use  of  oxone 
(a  commercial  form  of  sodium  peroxide)  is'  recommended  on  ac- 
count of  its  convenience  and  relatively  low  cost.  By  adding  water 
from  time  to  time  in  small  amounts  to  a  few  small  lumps  of  oxone 
in  a  flask,  a  free  flow  of  oxygen  may  be  kept  up  or  renewed  as  needed. 
A  thistle  funnel,  or  better  a  small  dropping  funnel,  through  one  of 
the  two  holes  of  the  stopper  will  serve  for  the  admission  of  the 
water,  the  other  hole  being  provided  with  a  delivery  tube. 

In  connection  with  the  study  of  kindling  points  (Section  41)  a  simple 
lecture  table  experiment  will  serve  to  make  the  matter  more  real 
to  the  pupils.  Bits  of  (a)  yellow  phosphorus,  (6)  sulphur,  and  (c) 
charcoal  may  be  used.  The  charcoal  can  usually  be  ignited  only  by 
direct  application  of  the  flame  to  a  projecting  corner  of  the  piece. 
The  good  heat  conductivity  of  a  copper  plate  will  suffice  to  raise  the 
temperature  of  the  phosphorus  and  sulphur  to  the  kindling  point 
without  contact  with  the  flame.  This  should  be  pointed  out  to  the 
class,  as  most  pupils  think  that  contact  with  an  open  flame  is  neces- 
sary for  ignition.  As  a  familiar  example  of  differences  in  kindling 
point,  cite  the  common  match  with  sulphide  of  phosphorus l  on  the 
tip,  an  easily  kindled  gunpowder-like  mixture  next,  and  then  paraf- 
fin and  wood  to  progressively  kindle  from  the  heat  of  the  burning 
substances  first  kindled.  The  safety  match  should  also  be  ex- 
plained. The  advantage  of  the  higher  kindling  point  and  non-poi- 
sonous character  of  red  phosphorus  should  be  emphasized.  Explain 
the  ingenious  placing  of  the  red  phosphorus  on  the  lighting  surface 
instead  of  on  the  tip  of  the  match. 

In  connection  with  the  study  of  oxygen  considerable  class  time 
should  be  given  to  relating  active  combustion  with  the  slower  forms 
such  as  combustion  in  the  body,  rusting  of  metals,  and  decay  of 
organic  matter. 

In  connection  with  the  paragraph  on  spontaneous  combustion 
(Section  43,  p.  46)  the  nature  of  the  drying  of  paints  can  be  explained. 
It  consists  in  the  oxidation  of  the  liquid  oil,  usually  linseed  oil,  to 
a  solid  resinous  substance  which  adheres  to  the  surface  and  binds 

1  The  use  of  yellow  phosphorus,  on  account  of  its  poisonous  properties,  is 
now  prohibited  by  law  in  the  United  States.  The  sulphide  of  phosphorus 
kindles  as  easily  but  it  is  not  poisonous. 


PAGES  38-49  21 

together  the  coloring  pigment.  Of  course  this  drying  oxidation 
does  not  use  as  much  oxygen  as  the  rapid  burning  of  the  oil,  which 
would  yield  carbon  dioxide  and  water  as  products.  The  resinous 
substance  is  not  especially  subject  to  further  slow  oxidation,  but 
of  course  if  it  were  heated  to  its  kindling  temperature,  it  would 
burn  like  any  resin  to  carbon  dioxide  and  water.  To  facilitate  the 
drying  oxidation  of  the  oils  certain  substances  called  driers,  usually 
containing  manganese  dioxide  or  lead  oxide,  are  added,  but  these 
driers  do  not  themselves  furnish  oxygen  to  the  oil ;  they  merely 
facilitate  the  addition  of  atmospheric  oxygen.  The  driers  act  as 
catalyzers  just  as  the  manganese  dioxide  acted  in  the  decomposition 
of  potassium  chlorate,  although  in  one  case  the  reaction  is  the  addi- 
tion of  oxygen  and  in  the  other  case  the  breaking  away  of  oxygen. 

The  practical  methods  of  preserving  foods  from  decay  (such  as 
are  briefly  indicated  in  Question  12,  p.  49)  should  be  gone  into  in 
class  and  explained  in  some  detail.  The  importance  of  decay  as 
a  means  of  removing  organic  matter  that  would  otherwise  become 
obnoxious  should  also  be  shown.  This  will  lead  naturally  to  the 
first  topic  of  the  next  chapter. 

The  kind  of  correlation  between  chemistry  and  daily  life  that 
is  advocated  in  the  above  paragraph  is  very  valuable  and  easily 
possible.  It  will  be  found  far  more  worth  while  than  the  mere 
teaching  of  the  facts  without  relating  them  to  the  general  principles 
concerned. 

Answers  to  Questions  on  Chapter  V 

Page  48 

1.  The  most  prominent  chemical  property  of  oxygen  is  its  ability 
to  react  vigorously  with  many  substances  when  they  are  heated  in 
contact  with  it.     It  should  be  noted,  however,  that  at  ordinary  tem- 
perature oxygen  is  practically  without  action  in  almost  all  cases  if 
no  moisture  is  present,  but  that  it  reacts  slowly  in  many  cases  when 
water  is  present. 

2.  See  answers  to  Questions  2  and  3,  Chapter  IV. 

3.  Gold  does  not  unite  directly  with  oxygen  under  any  conditions. 
It  must  be  that  gold  is  much  less  active  than  most  metals  towards 
oxygen. 


22  OXYGEN 

4.  The  use  of  pure  oxygen  in  the  blacksmith's  bellows  would 
produce  so  violent  a  fire  that  even  the  iron  put  in  the  fire  to  be  heated 
would  be  burned. 

6.  If  the  atmosphere  consisted  of  pure  oxygen,  a  fire  once  started 
would  be  so  violent  that  it  could  not  be  checked.  It  would  even 
consume  iron  and  some  other  materials  used  in  fireproof  construc- 
tion. 

6.  The  fire  danger  in  wooden  buildings  is  slight  for  the  reason 
that  the  kindling  temperature  of  wood  is  fairly  high. 

7.  Conditions  under  which  fires  start  without  the  application  of 
flame  are  discussed  under   spontaneous  combustion,  Section  43, 
p.  46. 

8.  Oxygen  is  not  lighter  than  air  and  hence  would  not  be  of  use 
for  filling  balloons. 

9.  Fish  breathe  by  withdrawing  oxygen  from  water.     Goldfish 
would  probably  die  if  they  were  placed  in  freshly  distilled  water. 
Before  the  water  in  a  retort  (see  Fig.  1,  p.  17)  begins  to  distill  actively, 
it  must  rise  to  100°  C.,  at  which  temperature  practically  all  of  the  dis- 
solved oxygen  is  driven  out,  for  the  solubility  of  gases  in  water  is 
less  at  higher  temperatures  (see  top  of  p.  43).     When  steam  begins 
to  pass  over  into  the  condensing  tube,  the  oxygen  is  driven  out  and 
the  condensed  water  in  trickling  down  the  tube  and  falling  into  the 
receiver  does  not  stay  long  enough  in  contact  with  the  air  to  dis- 
solve sufficient  oxygen  to  keep  fish  alive. 

10.  A  fallen  tree  in  the  forest  gradually  disappears  due  to  decay 
(Section  45,  p.  47). 

11.  Water  contaminated  with  sewage  is  unfit  to  drink  on  account 
of  poisonous  substances  in  the  sewage  and  especially  on  account  of 
the  germs  (bacteria,  microscopic  living  organisms)  of  dangerous 
diseases  which  may  be  present  if  the  sewage  comes  from  infected 
persons.     If  the  water  runs  for  miles  over  rapids  in  a  river,  it  be- 
comes thoroughly  oxygenated,  the  poisonous  materials  are  oxidized 
to  harmless  substances,  and  the  bacteria  are  killed. 

12.  Although  the  spoiling  of  food  products  is  similar  to  the  decay 
of  wood  in  that  it  takes  place  almost  solely  through  the  agency 
of  microscopic  life,  it  should  be  recognized  that  the  most  dangerous 
decompositions  of  foods  occur  in  the  absence  of  free  oxygen  and  are 


PAGES  50-66  23 

not  oxidations.  Nevertheless  anything  which  kills  these  little  or- 
ganisms will  prevent  the  spoiling  of  food,  as  well  as  the  decay  of 
wood. 

(a)  Canning  excludes  oxygen  and  also  excludes  bacteria.  At  the 
time  the  cans  are  sealed  the  contents  are  always  hot  so  that  no  live 
bacteria  are  sealed  up.  Effective  heating  kills  all  living  organisms. 

(6)  The  creosote  in  smoke  kills  bacteria. 

(c)  Salt  kills  bacteria. 

(d)  Bacteria  cannot  grow  and  multiply  when  cold,  but  simply 
lie  dormant.     Hence  refrigeration  retards  the  spoiling  of  food. 

(e)  Bacteria  can  grow  and  multiply  only  in  presence  of  water.     If 
dry,  they  simply  remain  dormant.     Hence  drying  prevents  spoiling. 

(/)  Neither  can  bacteria  thrive  in  concentrated  sugar  solutions, 
although  many  organisms  like  yeasts  live  principally  on  sugars  when 
the  latter  are  diluted  with  water.  Hence  sirup,  which  is  a  highly 
concentrated  solution  of  sugar,  prevents  the  development  of  micro- 
scopic organisms. 


CHAPTER  VI 

THE    OXIDES    OF    CARBON 

Pages  50-66 

THE  carbon  dioxide  cycle  in  nature  should  receive  more  time  in 
class  than  can  be  devoted  to  it  in  the  textbook.  Those  pupils  who 
have  previously  studied  botany  can  be  called  upon  to  explain  the 
necessary  outlines  of  plant  structure  and  plant  physiology.  The 
large  part  played  by  decay,  brought  about  by  bacteria,  cannot 
be  over-emphasized.  Bacteria  are  to  be  classed  as  plants  rather 
than  as  animals  and  it  should  be  pointed  out  how  extremely  small 
a  part  in  the  great  carbon  dioxide  cycle  is  played  by  animals,  for 
animals  and  fires  together  produce  only  about  three  per  cent  of  all 
the  carbon  dioxide  returned  to  the  air. 

In  most  classes  all  pupils  will  be  given  a  chance  to  prepare  carbon 
dioxide  and  to  study  it  at  first  hand.  All  laboratory  manuals  con- 
tain full  directions  for  this  work.  If  a  siphon  of  plain  soda  can  be 


24  THE  OXIDES  OF  CARBON 

had,  pupils  can  more  readily  learn  the  properties  of  the  water  solu- 
tion of  carbon  dioxide.  Each  pupil  will  need  no  more  than  a  few 
c.c.  of  the  solution.  The  effect  of  one  drop  of  the  solution  on  some 
lime  water  in  a  test  tube  and  then  the  effect  of  adding  a  slight  excess 
of  the  carbonated  water,  should  be  noted.  The  greater  solubility 
of  the  calcium  bicarbonate  thus  formed  should  be  explained  and 
the  knowledge  applied  to  the  formation  of  limestone  caves  and  the 
causation  of  one  type  of  hard  water  (temporary  hardness).  This 
matter  can  then  be  gone  into  more  thoroughly  under  calcium  and 
its  compounds  (Sections  211-214,  pp.  199-203),  when  the  pupil 
has  more  chemistry  at  his  command  and  can  better  understand  the 
nature  of  the  reactions  involved.  The  preliminary  approach  to 
the  subject  in  connection  with  this  chapter  will  give  something  to 
which  the  more  complete  treatment  later  on  can  be  attached. 

Because  of  the  many  valuable  points  of  contact  between  some  of 
the  carbon  dioxide  chemistry  and  daily  life,  it  is  well  to  spend  quite 
a  little  time  on  such  topics  as  the  chemical  fire  extinguisher,  car- 
bonated waters,  the  use  of  yeast,  and  the  use  of  baking  powder. 
If  a  chemical  extinguisher  is  available,  it  should  by  all  means  be 
taken  apart  in  the  presence  of  the  pupils,  and  if  practicable  it  should 
be  discharged  at  a  small  fire  built  in  the  school  yard.  Such  an  ex- 
periment will  arouse  much  interest  and  will  be  remembered  long 
after  most  of  the  more  theoretical  parts  of  the  course  have  been  for- 
gotten. It  has  its  practical  value  too,  for  every  one  should  know 
what  to  do  in  case  of  fire  and  how  to  use  extinguishers  if  they  are 
available.  The  cooling  effect  of  the  water  thrown  by  the  carbon 
dioxide  type  of  extinguisher  should  be  emphasized.  It  is  probably 
of  more  importance  than  the  smothering  effect,  especially  in  outside 
fires,  where  the  action  of  the  wind  prevents  much  smothering. 

In  connection  with  the  commercial  manufacture  of  carbon  dioxide 
(Section  61,  p.  62),  it  may  be  added  that  much  carbon  dioxide  for 
use  in  preparing  soda  water  is  being  made  at  the  present  time  by 
the  combustion  of  coke.  Such  charged  water  does  not  carry  any  of 
the  yeasty  odor  sometimes  noted  in  the  product  from  the  breweries. 

The  brief  treatment  of  carbon  monoxide  (Section  62,  p.  62  and  Sec- 
tion 65,  p.  63)  serves  to  introduce  the  subject  of  multiple  combining 
proportions  and  to  give  a  slight  acquaintance  with  the  properties 


PAGES  67-78  25 

of  the  lower  oxide  of  carbon.  This  acquaintance  can  later  be  re- 
called when  producer  gas  and  water  gas  are  to  be  studied  (Sections 
283-284,  pp.  270-273). 

Answers  to  Questions  on  Chapter  VI 

Page  65 

In  this  chapter  no  question  is  asked  except  to  recall  or  illustrate 
a  practical  use  of  information  clearly  given  in  the  textbook. 


CHAPTER  VII 

THE   ATMOSPHERE   AND    NITROGEN 

Pages  67-78 

THE  experiments  on  air  which  make  use  of  yellow  phosphorus 
should  be  performed  by  the  teacher  on  account  of  the  danger  of 
serious  burns. 

The  classroom  discussion  of  the  fixation  of  nitrogen  affords  a 
valuable  means  of  correlating  chemistry  and  daily  life.  A  little 
volume,1  which  has  recently  been  published,  will  be  of  value  to  the 
teacher  in  preparing  himself  for  an  up-to-date  discussion  of  this 
subject. 

In  performing  the  more  accurate  experiment  on  the  volume  of 
oxygen  in  air  (Section  78,  p.  74),  it  will  be  found  advantageous  to 
leave  the  apparatus  standing  overnight.  The  use  of  phosphorus 
rather  than  alkaline  pyrogallate  solution  is  recommended,  as  pupils 
can  much  more  readily  comprehend  what  is  taking  place  in  the 
former  reaction. 

The  above  experiment  leads  naturally  to  the  use  of  Boyle's  and 
Charles'  laws.  It  will  be  found  that  pupils  will  learn  to  use  these 
laws  much  more  readily  when  they  thus  have  a  real  need  for  the 
application  of  them. 

1  Knox,  The  Fixation  of  Atmospheric  Nitrogen.  D.  Van  Nostrand  Com- 
pany. 


26  THE  ATMOSPHERE  AND  NITROGEN 

Answers  to  Questions  on  Chapter  VII 

Page  78 

•  1.  It  will  be  recalled  that  the  chief  characteristics  of  a  chemical 
compoun^Las  distinguished  from  a  mixture  are :  (1)  that  its  proper- 
ties are  altogether  different  from  the  properties  of  its  constituent 
elements  when  separate,  (2)  that  heat  is  either  given  off  or  absorbed 
when  it  is  formed  from  its  constituents,  (3)  that  the  proportion  of  its 
constituents  is  always  the  same. 

The  facts  stated  in  Section  71,  p.  69,  in  support  of  the  assertion 
that  air  is  a  mixture  rather  than  a  chemical  compound,  show  that 
air  does  not  possess  these  characteristics  of  a  compound.  As 
additional  facts  may  be  mentioned  : 

(1)  Air  may  be  separated  by  the  physical  process  of  distilling 
liquefied  air  (Section  33,  p.  40).     This,  however,  in  itself  is  not  a 
complete  proof.     We  know,  for  example,  when  oxide  of  mercury, 
which  is  undeniably  a  compound,  is  subjected  to  the  same  sort  of 
physical  treatment,  namely,  heating,  that  it  is  decomposed  and 
oxygen  passes  off  first.     But  we  know  in  the  latter  case  that  the  two 
products  bear  no  resemblance  to  the  red  mercuric  oxide,  and  that 
the  products  are  always  yielded  in  the  same  proportion.     When 
liquid  air  is  distilled,  nitrogen  first  passes  off  fairly  pure,  but  the  pro- 
portion of  oxygen  gradually  increases,  until  towards  the  last  nearly 
pure  oxygen  is  passing  off.     The  liquid  left  in  the  vessel  shows  no 
constant  composition,  but  its  proportion  of  oxygen  increases  steadily. 
Thus  characteristics  1  and  3  of  compounds  are  again  shown  not  to 
be  found  with  air. 

(2)  Air  is  soluble  in  water,  but  air  obtained  from  water  which  held 
it  in  solution  has  a  different  composition  from  the  air  originally 
dissolved.     The  oxygen  and  nitrogen  of  the  air  dissolve  in  water 
in  the  ratio  of  their  solubilities,  but  this  ratio  is  different  from  that 
in  which  they  occur  in  normal  air.     If  air  were  a  compound,  air  ob- 
tained from  solution  would  not  vary  in  composition  from  that 
which  was  dissolved. 

(3)  A  more  everyday  argument  is  that  air  exhaled  from  the  lungs 
contains  a  lesser  proportion  of  oxygen  than  ordinary  air.     Yet  this 
exhaled  air  is  still  practically  air.     This  air  can  be  passed  through 


PAGES  67-78  27 

a  tube  filled  with  caustic  soda  (see  Fig.  2,  p.  28)  whereby  the  carbon 
dioxide  is  removed.  The  air  then  has  practically  the  same  proper- 
ties as  ordinary  air.  It  can  support  combustion  and  respiration 
almost  as  well  as  ordinary  air.  Yet  the  composition  is  different. 
Thus  again  it  is  shown  that  air  does  not  possess  characteristic  3  of 
compounds. 

2.  The  gases  present  in  the  air  are  :  Nitrogen,  about  78  per  cent 
by  volume;  oxygen,  about  21  per  cent;  argon,  about  1  per  cent; 
carbon  dioxide,  about  0.04  per  cent;   minute  quantities  of  helium, 
neon,  krypton,  and  xenon;  and  water  vapor  in  amounts  varying 
from  very  little  in  desert  regions  to  2  per  cent  or  even  more  in  very 
warm  and  moist  air. 

3.  Oxygen  is  the  most  important  of  these  gases  from  the  stand- 
point of  its  direct  activity  and  the  amount  of  it  involved  in  processes 
which  are  vital  to  human  life  and  welfare.     The  human  being  could 
not  live  many  minutes  without  oxygen  to  breathe.     Neither  would 
fuels  burn  without  oxygen. 

But  water  vapor,  carbon  dioxide,  and  nitrogen  are  also  absolutely 
essential  to  the  human  race  as  it  has  become  adapted  through  long 
ages  to  its  present  environment.  Indeed  we  can  hardly  say  that 
any  one  of  these  gases,  not  even  excepting  oxygen,  is  more  important 
than  any  one  of  the  others,  for  human  life  could  not  long  continue 
if  any  one  of  these  gases  should  disappear  from  the  atmosphere. 

Water  vapor,  through  occasional  condensation  as  rain,  supplies 
the  land  with  the  moisture  necessary  to  the  growth  of  crops.  Car- 
bon dioxide  also  is  necessary  to  the  growth  of  plants  (Section  48, 
p.  50).  The  direct  service  of  nitrogen  is  in  diluting  the  oxygen  of 
the  air,  thus  moderating  the  intensity  of  the  combustion  of  fuels. 
Nevertheless  without  nitrogen  it  might  be  possible  to  dampen  the 
combustion  of  fuels  by  redesigning  our  furnaces  with  smaller  drafts. 
The  vital  service  of  nitrogen,  however,  is  an  indirect  one.  Through 
various  means  of  fixation,  some  of  which  are  mentioned  in  the 
chapter,  the  supply  of  combined  nitrogen  in  the  soil  is  maintained. 
This  combined  nitrogen  is  essential  to  the  growth  of  plants,  and  thus 
if  the  nitrogen  should  disappear  from  the  air,  our  crops  would  cease 
to  grow  after  a  period  of  years  when  the  soil  had  become  exhausted 
of  its  nitrogen  compounds. 


28  THE  ATMOSPHERE  AND   NITROGEN 

Argon  and  the  similar  gases,  helium,  neon,  krypton,  and  xenon, 
are  of  no  known  importance  in  the  development  of  human  life  or 
of  any  other  form  of  living  matter. 

4.  The  fixation  of  nitrogen  is  difficult  because  nitrogen  is  an 
inactive  element,  or  in  other  words,  it  has  little  or  no  tendency  to 
combine  with  the  elements  or  substances  with  which  it  ordinarily 
comes  in  contact.  Nitrogen  once  in  combination,  however,  passes 
from  one  form  of  combination  to  another  with  considerable  ease. 
Thus  combined  nitrogen  can  undergo  the  changes  necessary  to  bring 
it  into  the  forms  required  by  the  various  kinds  of  plant  and  animal 
life. 

6.  In  nature,  atmospheric  nitrogen  is  brought  into  combination 
mainly  through  the  action  of  colonies  of  bacteria  which  live  on  the 
roots  of  the  plants  of  the  legume  family.  Electrical  storms  cause  the 
combination  of  some  nitrogen  with  oxygen  in  the  air  and  subsequently 
nitric  acid  is  formed  and  brought  down  to  the  soil  with  the  rain. 

6.  See  Section  75,  p.  71. 

7.  Oxygen  can  be  removed  from  the  air  by  allowing  any  substance 
with  which  it  will  form  a  non-gaseous  compound  to  act  on  the  air. 
As  stated  in  the  textbook,  phosphorus  may  be  burned  in  the  air,  or 
better,  wet  phosphorus  may  be  allowed  to  oxidize  slowly.     One  of 
the  best  methods  of  removing  oxygen  from  air  is  to  pass  the  air 
through  a  tube  containing  copper  turnings  heated  to  redness.     Iron 
turnings  will  serve  as  well  if  the  air  be  free  of  water  vapor,  upon 
which  the  iron  will  also  act,  setting  free  hydrogen  (see  Section  100, 
p.  100). 

8.  In  ordinary  fires  four  volumes  of  nitrogen  have  to  be  heated  to 
the  temperature  of  the  fire  for  every  one  volume  of  oxygen.     This 
of  course  decreases  the  temperature  of  the  fire  and  it  provides  a 
greater  quantity  of  gas  to  carry  unutilized  heat  up  the  chimney. 
If  pure  oxygen  were  used  instead  of  air,  the  higher  temperature  of 
the  fire  would  occasion  a  more  rapid  transfer  of  heat  to  the  boiler 
tubes  (see  Fig.  4,  p.  35)  and  there  would  be  but  approximately  one 
fifth  as  much  gas  to  carry  waste  heat  up  the  chimney. 

The  objections  to  such  a  use  of  oxygen  are  first  its  expense  and 
second  its  effect  on  the  furnace.  Iron  itself  burns  freely  at  tempera- 
tures above  its  kindling  point.  Its  combustion  in  pure  oxygen  is, 


PAGES  67-78 


29 


as  we  know,  self-sustaining.  To  use  pure  oxygen,  the  furnace  would 
have  to  be  redesigned.  No  iron  could  be  used  in  the  construction 
of  the  grate,  dome,  or  even  door.  The  water-cooled  boiler  tubes, 
however,  could  still  be  of  iron  because  their  temperature  could  not 
reach  the  kindling  point  since  they  are  filled  with  water.  Further- 
more, it  would  be  very  difficult  to  find  a  fire  brick  which  would  not 
melt  under  the  heat  of  such  a  fire. 

9.  The  following  table  taken  from  Woodman  and  Norton,  Air, 
Water  and  Food,  Wiley  and  Company,  gives  the  per  cent  of  nitroge- 
nous substance  in  some  common  kinds  of  food.  The  values  are 
based  on  the  weight  of  the  food  as  bought,  including  in  a  number 
of  cases  a  large  proportion  of  water.  The  nitrogenous  substance 
contains  on  an  average  16  per  cent  of  actual  nitrogen. 


FOOD  MATERIAL 

NITROGENOUS  SUBSTANCE 

Beef  (round) 

Per  Cent 
192 

Beef  (sirloin  steak)   . 

165 

Veal  (breast)  . 

14  2  to  16  9 

Fresh  pork  (ribs  and  shoulder)  . 
Chicken  (fowls)   
Medium  fat  mutton  and  beef    . 
Salt  cod  (boneless)    

13.7  to  14.5 
11.5  to  16.0 
11.4  to  12.9 

277 

Sardines  (canned) 

237 

Herring  (smoked) 

20  5 

Salmon  (canned) 

18  6  to  20  2 

Salt  mackerel  . 

163 

Salmon  (fresh) 

12  6  to  15  0 

Fish  (fresh) 

11  9  to  12  0 

Eggs  . 

11  9 

Milk  

3  3 

Cheese  (American  pale)     .     .     . 
Cheese  (Neuchatel)  
Butter    

28.8 
15.1  to  22.3 
1  0 

Peanut  butter 

293 

30  THE  GAS  LAWS 


FOOD  MATERIAL 


NITROGENOUS  SUBSTANCE 


Peas  (dried) 

Beans  (dried) 

Peanuts 

Walnuts  (shelled)      .     .     . 

Oats 

Macaroni 

Wheat  (entire)  flour      .     . 
Wheat  flour  (white,  bakers') 
Raisins  . 


Per  Cent 

20.4  to  28.0 
19.9  to  26.6 

19.5 

16.6 

16.5 
7.9  to  16.6 

12.2  to  14.6 

10.3  to  14.9 
2.3 


10.  Clover  and  alfalfa  are  members  of  the  legume  family  and  are 
particularly  suited  for  increasing  the  soil  content  of  combined 
nitrogen. 

CHAPTER  VIII 

THE    GAS    LAWS 

Pages  79-90 

THE  explanation  of  the  gas  law  corrections  has  purposely  been 
made  in  considerable  detail,  as  experience  has  shown  that  what 
is  obvious  to  the  teacher  is  often  far  from  obvious  to  the  pupil. 
Where  pupils  have  previously  had  work  in  physics  on  Boyle's  and 
Charles'  laws  less  time  will  be  needed,  but  they,  too,  usually  profit 
from  a  review  of  the  work. 

It  is  difficult  to  teach  how  to  correct  for  the  presence  of  water 
vapor  so  that  this  subject  will  be  really  comprehended  by  the  pupil. 
The  authors  deem  it  wiser  to  avoid  the  subject  altogether  than  to 
teach  it  in  a  mere  mechanical  fashion,  and  particularly  so  since  the 
refinement  of  any  experiments  likely  to  be  undertaken  will  not  be 
great  enough  to  make  the  water  vapor  corrections  of  importance. 
Hence  the  subject  of  water  vapor  corrections  has  been  omitted  in 
the  text.  It  is  given  in  Sections  I  and  II  of  the  Appendix  and  it 


PAGES  79-90  31 

is  certainly  well  worth  teaching  if  the  teacher  can  take  the  time  to 
teach  it  well.  If  it  is  well  taught,  the  pupil  not  only  will  be  able  to 
use  correctly  aqueous  tensions  in  calculating  gas  volumes  to  stand- 
ard conditions,  but  he  will  perceive  their  bearing  on  the  subjects  of 
relative  humidity,  evaporation,  and  precipitation. 

Answers  to  Questions  on  Chapter  VIII 

Page  89 


2-50xlfTfr48-3c-c- 


5.    100  X         =  200  c.c.  6.   200  X          -  194.7  c.c. 
273  7oO 

7.    100  X  ^  =  102.6  c.c.  8.   40.1  X  ^  =  38.0  c.c. 

9.     20  X  —  =  21.1  c.c.  10.    100  X  —  =  50.0  c.c. 
740  1520 


13   55  x 


15.   New  temp.  =  273  X  2  =  546°  Abs.  =  273°  C. 
New  press.  =  760  X  2  =  1520  mm. 
Ans.     Final  conditions  are  273°  C.  and  1520  mm. 


32  WATER 

CHAPTER  IX 

WATER 

Pages  91-99 

THIS  preliminary  chapter  on  water  deals  with  it  primarily  from 
the  side  of  its  physical  properties  and  its  common  uses.  While 
not,  strictly  speaking,  a  chemical  treatment  of  water,  the  chapter 
nevertheless  deals  with  matters  of  the  greatest  importance,  not 
only  to  chemists  but  to  every  one.  A  chemistry  course  can  hardly 
afford  to  omit  such  a  study  of  water.  As  most  chemical  reactions 
are  conducted  in  water  solution,  the  subject  of  solubility  should 
receive  even  more  attention  than  is  given  it  in  this  chapter.  It  will 
be  advisable  to  let  the  pupils  make  several  simple  experiments  of 
a  roughly  quantitative  character  in  order  to  determine  for  them- 
selves the  simpler  facts  of  solubility. 

The  use  of  experiments  which  lead  to  practical  applications  will 
arouse  more  interest  on  the  part  of  the  pupils.  For  example,  if 
gasoline  is  used  by  the  pupil,  together  with  grease,  to  show  the 
solubility  of  the  latter  in  gasoline,  the  pupil  can  then  readily  un- 
derstand why  gasoline  is  used  in  cleaning  clothing.  It  would  be 
well  to  have  the  pupils  remove  grease  spots  from  cloth  by  the  use  of 
gasoline.  Some  members  of  the  class  might  use  carbon  tetrachlo- 
ride,  ether,  or  benzol  similarly  and  report  to  the  class.  The  fact  that 
all  these  solvents  are  in  practical  use  for  cleaning,  or  for  extracting 
fats,  should  be  brought  out.  The  use  of  some  of  these  solvents 
in  extracting  grease  from  garbage  on  a  large  scale  may  be  men- 
tioned. 

The  insolubility  of  grease  in  water  should  of  course  be  first 
learned  by  actual  test.  Similarly  the  difference  in  solubility  of 
sugar  in  hot  and  cold  water  may  be  shown  experimentally,  and 
related  to  candy  making  and  to  the  crystallization  of  granulated 
sugar  by  the  refineries. 

The  slight  solubility  of  some  substances,  as  compared  to  others, 
may  be  shown  by  contrasting  the  ready  solubility  of  sugar  with  the 
slight  solubility  of  crystals  of  boric  acid.  The  use  of  the  saturated 


PAGES  91-99  33 

solution  of  the  latter  as  an  eyewash  may  be  mentioned.  The  very 
slight  solubility  of  boric  acid  serves  as  a  guide  in  making  up  the 
solution,  for  by  shaking  the  crystals  in  cold  water  it  is  not  possible 
to  get  too  much  for  the  purpose  into  solution. 

Supersaturation  may  be  studied  briefly  in  passing,  in  order  to 
lead  to  a  brief  study  of  crystallization,  which  may  well  be  made 
in  connection  with  the  solubility  work.  Chemists  depend  so  largely 
on  recrystallization  to  purify  substances,  that  a  few  experiments  in 
the  forming  of  crystals  will  be  well  worth  while. 

The  use  of  common  alum  for  this  purpose  is  recommended  and 
fine  large  perfect  crystals  can  be  obtained  by  the  pupils  if  a  little 
care  is  used.  Perhaps  the  best  way  to  proceed  is  to  have  each  pu- 
pil prepare  about  200  c.c.  of  hot  alum  solution  containing  about 
25  g.  of  alum  and  to  allow  this  to  slowly  cool.  A  wrapping  of 
towels  or  aprons  around  the  flasks  will  permit  slow  cooling,  or  a 
number  of  the  flasks  can  be  shut  up  in  a  fireless  cooker,  if  one  is 
available. 

The  excess  of  material  will  form  fairly  perfect  crystals  during 
the  cooling,  and  these  may  be  used  as  seed  crystals  in  the  remain- 
ing saturated  solution,  which  should  be  transferred  to  beakers  or 
crystallizing  dishes  to  permit  evaporation  of  the  water.  The  grow- 
ing crystals  should  be  turned  to  lie  on  new  sides  each  day,  or  they 
may  be  suspended  in  a  noose  of  thread  so  as  to  grow  symmetrically. 
In  the  latter  case  the  thread  will,  of  course,  remain  in  the  com- 
pleted crystal.  Much  interest  will  be  aroused  by  such  an  experi- 
ment as  above  outlined,  and  no  more  than  a  few  minutes  each  day 
will  be  required  for  it.  A  few  of  the  pupils  may  use  copper  sulphate 
or  nickel  nitrate  in  small  amounts  to  vary  the  experiment,  and  the 
beautiful  blue  or  green  crystals  will  prove  very  attractive  to  the 
class. 

The  brief  treatment  of  atmospheric  moisture  in  Sections  94-95, 
pp.  93-95,  although  belonging  more  properly  to  another  branch  of 
science,  has  valuable  practical  applications  which  are  so  dependent 
on  an  important  property  of  water,  namely,  its  varying  vapor  ten- 
sions at  different  temperatures,  that  it  deserves  a  place  in  this 
chapter.  For  those  who  teach  the  correction  for  aqueous  tension 
in  connection  with  gas  law  work,  this  matter  of  relative  humidity 


34  WATER 

has  a  direct  application  and  may  be  used  with  the  matter  on  page 
426  in  the  Appendix  (see  footnote,  p.  86).  A  visit  to  the  local 
weather  bureau  station  and  the  reading  of  the  hygrometer  will  be  of 
interest. 

As  an  additional  classroom  exercise,  the  effect  on  the  mucous 
membranes  of  the  respiratory  tract  of  too  low  a  relative  humidity 
in  over-heated  air  may  well  be  taken  up,  and  the  use  of  various 
schemes  for  humidifying  the  air  of  public  buildings  should  be  men- 
tioned. 

The  treatment  of  the  subject  of  water  purification  given  in  Sections 
96-98,  pp.  95-97,  is  of  course  very  brief  and  may  well  be  supple- 
mented by  class  discussion.  The  difficult  biological,  chemical,  and 
especially  mechanical  problems  attendant  upon  the  actual  manage- 
ment of  a  public  water  supply  cannot  be  more  than  touched  upon 
in  a  high  school  course  in  chemistry.  It  would  be  unfair  to  the 
pupils  to  pretend  that  they  can  become  expert  in  these  difficult 
matters.  A  trip  to  the  municipal  filter  plant  and  water  laboratory 
is  always  of  interest  at  this  point.  A  brief  hint  at  the  general  cause 
of  the  hardness  of  water  is  given  in  Section  99,  p.  97,  to  establish 
a  slight  foothold  for  future  progress,  when  hard  water  is  studied 
more  at  length  in  Sections  213-214,  p.  201. 

Answers  to  Questions  on  Chapter  IX 

Page  98 

1.  A  colorless  liquid  which  appeared  like  water  could  be  proved 
to  be  water  if  its  specific  gravity  were  found  to  be  exactly  one,  or  if 
it  froze  at  exactly  0°  C.,  or  boiled  at  exactly  100°  C. 

2.  Ice  could  be  most  quickly  distinguished  from  rock  crystal 
(quartz)  by  its  hardness.     The  former  is  easily  scratched  with  a 
knife,  the  latter  not  at  all. 

3.  We  can  prove  that  water  vapor  is  present  in  the  schoolroom 
by  watching  it  condense  on  a  cold  surface,  as  the  side  of  a  dipper  or 
tumbler  filled  with  ice  water  or  a  mixture  of  salt  and  ice. 

4.  See  Section  92,  p.  92. 

6.   Nitrogen  compounds,  as  well  as  compounds  of  potassium  and 


PAGES  91-99  35 

phosphorus,  must  be  soluble,  at  least  to  some  extent,  to  be  available 
for  plant  nutrition.  Hence  if  our  western  deserts  had  been  subjected 
to  rainfall  during  the  last  century,  much  of  the  soluble  plant  food 
would  have  been  washed  out,  and  the  land  would  not  show  the 
fertility  that  it  now  does. 

6.  In  the  daytime,  the  sun  warms  the  earth's  surface  and  a  good 
deal  of  water  evaporates  into  the  likewise  warmed  lower  layer  of 
the  atmosphere.     At  night  the  lower  layer  of  the  atmosphere  be- 
comes cooler  and  incapable  of  holding  as  much  water  vapor.     Part 
of  the  latter  therefore  condenses  and  appears  as  dew  (see  Section  94, 
p.  93).     If  the  subject  of  the  pressure  of  saturated  water  vapor  has 
been  taught  in  connection  with  the  corrections  for  gas  volumes,  it 
should  also  be  applied  in  answering  this  question  (see  Appendix  I 
and  II,  pp.  425-427). 

7.  See  Section  95,  p.  95. 

8  and  9.   See  Sections  96,  97,  pp.  95-96. 

10.  The  human  body  requires  a  certain  quantity  of  mineral  salts 
for  its  nutrition,  and  these  may  be  obtained  from  drinking  water 
as  well  as  from  solid  food.     But  mineral  salts  will  remain  as  a  solid 
scale  in  boiler  tubes  when  the  water  is  converted  to  steam,  and  they 
may  interact  with  the  soap  used  in  laundries,  thereby  using  up  the 
soap  and  producing  a  troublesome  precipitate. 

Bacteria,  on  the  other  hand,  work  no  injury  in  most  manufac- 
turing operations,  for  they  find  no  fertile  ground  for  multiplying. 
Even  if  they  do  by  chance  multiply,  the  poisons  that  they  secrete 
have  no  effect  on  the  inanimate  objects  with  which  they  come  in 
contact. 

Thus  the  same  standards  of  purity  do  not  apply  to  water  for 
drinking  and  for  industrial  uses. 

11.  To  obtain  fresh  water  for  drinking,  one  would  be  most  likely 
to  distill  salt  water.     Lacking  a  still,  however,  one  might  take  ad- 
vantage of  a  cold  night  or  of  an  ice  machine  to  freeze  the  water,  for 
it  is  to  be  noted  that  pure  ice  separates  from  salt  water  unless  the 
solution  is  saturated  and  sea  water  is  not  more  than  one  tenth  satu- 
rated with  salt. 


36  COMPOSITION   OF  WATER 

CHAPTER   X 

COMPOSITION    OF    WATER 

Pages  100-110 

THE  teacher  will  note  the  pedagogical  method  involved  in  con- 
necting the  investigation  of  the  composition  of  water  with  the 
previous  investigation  as  to  the  composition  of  air.  If  the  matter 
is  taken  as  a  sort  of  interesting  game,  as  a  difficulty  to  be  sur- 
mounted, the  pupils  will  frequently  apply  themselves  to  the  task 
with  surprising  eagerness.  The  material  first  used  in  the  attack 
upon  water  is  the  well-known  metal  iron,  which  with  the  aid  of  heat 
succeeds  in  decomposing  water. 

Draw  from  the  pupils  by  suitable  questions,  the  similarity 
between  the  product  formed  on  the  iron  this  time  and  that  formed 
when  iron  was  heated  in  air.  In  short,  establish  the  identity  of  the 
two  products  by  comparison  of  properties.  Let  this  be  done  in 
connection  with  a  classroom  experiment,  following  the  outline  of 
that  described  in  Section  100,  p.  100,  and  let  the  use  of  the  textbook 
by  the  pupils  follow  rather  than  precede  the  experiment. 

The  use  of  the  unfamiliar,  but  more  active  metal  sodium,  can 
then  follow.  (If  the  pupils  use  sodium,  the  usual  precautions,  as 
to  using  very  small  pieces  and  keeping  at  a  respectful  distance 
from  the  dish  in  which  the  reaction  takes  place,  should  be  ob- 
served.) The  teacher  may  use  bits  of  potassium  and  calcium 
to  illustrate  the  gradations  in  activity  among  the  very  active  metals, 
and  to  amplify  the  evidence  that  water  contains  hydrogen,  which  it 
gives  up  when  active  metals  react  with  it. 

The  use  of  zinc  dust  with  the  residue,  after  water  and  sodium 
have  reacted,  gives  another  chance  for  the  pupils  to  reason  out 
the  meaning  of  the  reaction.  It  also  enables  them  to  show  the 
double  character  of  the  hydrogen  of  water,  and  that  part  of  the 
hydrogen  is  more  readily  dislodged  than  the  rest  of  it. 

The  electrolysis  experiment  adds  to  the  evidence  in  regard  to  the 
composition  of  water  the  fact  that  oxygen  is  the  other  constituent, 
and  also  gives  the  volume  composition. 


PAGES  100-110  37 

The  synthesis  of  water  follows  to  confirm  the  volume  composition 
and  to  show  that  two  volumes  of  steam  result  from  two  volumes  of 
hydrogen  and  one  volume  of  oxygen.  The  weight  composition  is 
next  calculated  from  the  weight  per  liter  of  each  gas  and  the  volume 
composition. 

This  fairly  thorough  study  of  the  composition  of  water  is  given, 
to  be  later  used  as  a  basis  for  the  presentation  of  the  atomic  theory 
and  for  showing  how  a  formula  may  be  deduced.  Avogadro's  hy- 
pothesis is  also  to  be  used  in  connection  with  the  volume  relations 
here  brought  out. 

The  method  is  slow,  but  far  surer  to  produce  ultimate  under- 
standing than  a  more  rapid  but  superficial  covering  of  the  ground  ; 
and  there  is  surely  more  mental  discipline  to  be  had  from  the  slow 
but  more  thorough  method. 

The  brief  study  of  the  other  oxide  of  hydrogen,  hydrogen  perox- 
ide, comes  naturally  enough  after  the  study  of  water.  It  affords  an 
additional  case  of  multiple  proportions,  the  two  oxides  of  carbon 
having  previously  been  mentioned  in  Sections  62-65,  pp.  62-64. 

Answers  to  Questions  on  Chapter  X 
Page  109 

1.  We  know  that  water  cannot  be  an  element  because  it  can  be 
decomposed  into  two  substances,  hydrogen  and  oxygen,  the  com- 
bined weights  of  which  are  just  equal  to  the  weight  of  the  water. 

2.  The  explosion  of  an  oxygen-hydrogen  mixture  is  due  to  the 
expansion  caused  by  the  high  temperature  produced  during  the  re- 
action.    Except  for  this  expansion,  the  volume  of  the  water  vapor 
formed  is  less  than  the  sum  of  the  volumes  of  the  oxygen  and  hydro- 
gen concerned.     When  there  are  just  two  volumes  of  hydrogen  for 
each  volume  of  oxygen,  the  gases  combine  completely,  and  the  heat 
of  the  reaction  goes  solely  to  raising  the  temperature  of,  and  thus  ex- 
panding, the  water  vapor.     If  the  proportions  are  other  than  two  to 
one,  the  excess  of  either  one  gas  or  the  other  behaves  like  any  inactive 
gas.     Some  of  the  heat  of  the  reaction  goes  to  heating  this  excess 
and  so  the  temperature  of  the  mixture  does  not  rise  so  high,  the  ex- 
pansion is  less  sudden,  and  the  explosion  is  not  so  sharp. 


38  COMPOSITION   OF  WATER 

3.  See  Table  IV,  p.  428,  of  Appendix. 

4.  The  whole  of  the  30  c.c.  of  the  hydrogen  unites  with  15  c.c. 
of  the  oxygen,  leaving  15  c.c.  of  the  oxygen  unchanged.     The  volume 
of  the  water  is  negligible.    Answer,  15  c.c. 

6.  30  c.c.  of  hydrogen  combine  with  15  c.c.  of  oxygen,  forming  30 
c.c.  of  water  vapor  and  leaving  15  c.c.  of  oxygen.  Total  volume 
is  45  c.c.,  consisting  of  30  c.c.  of  water  vapor  and  15  c.c.  of  oxygen. 

6.  The  volume  of  the  tube  being  constant,  the  amounts  of  the 
gases  are  in  proportion  to,  and  can  be  measured  by,  the  pressures 
they  cause.     Hence  the  76  cm.  of  oxygen  will  combine  with  2  x  76 
=  152  cm.  of  hydrogen.     76  +  152  =  228  cm.  =  the  total  pressure 
of  the  mixture.     Hence  the  tube  contained  the  mixture  in  combining 
proportions.     After  the  explosion,  when  room  temperature  is  re- 
gained, there  will  be  a  few  drops  of  liquid  water  collected  on  the  walls 
of  the  tube,  and  the  rest  of  the  tube  will  be  filled  with  water  vapor  at 
a  low  pressure. 

7.  At  100°  C.,  10  cm.  of  oxygen  combine  with  20  cm.  of  hydrogen, 
forming  20  cm.  of  water  vapor  and  leaving  20  cm.  of  hydrogen. 
After  explosion,  the  pressure  is  40  cm.  at  100°  C. 

Cooled  to  0°  C.,  the  water  vapor  condenses  to  liquid,  and  we  neg- 
lect the  small  pressure  of  the  little  water  vapor  that  remains.  The 
pressure  of  the  hydrogen  decreases  in  proportion  to  the  absolute 
temperature : 

20  X  fit  =  14.6  cm.  =  pressure  at  0°  C. 

8.  Composition  by  weight :  hydrogen,  2.75%  ;  chlorine,  97.25%. 

9.  A  water  chemist's  business  is  to  test  the  suitability  of  water 
for  drinking  supply  or  for  industrial  purposes.     He  knows,  as  does 
every  chemist,  the  exact  composition  of  pure  water,  hence  there  is 
no  object  in  decomposing  the  water  to  find  out  how  much  hydrogen 
and  how  much  oxygen  will  be  obtained.     His  task  is  to  examine  the 
water  for  the  dissolved  and  suspended  substances  it  contains. 

10.  Water  is  used  largely  for  power  in  turning  mill  wheels  and 
turbines ;   in  mining  it  is  used  to  carry  gold  or  metal-bearing  sands 
over  plates  that  collect  the  metal ;    in  countless  industries  and  in 
agriculture  it  is  used  as  a  solvent;    and  in  all  of  these  cases  the 
water  is  not  decomposed.     It  is  decomposed  in  only  a  few  practical 
industries,  as,  for  example,  where  hydrogen  is  obtained  by  decompos- 


PAGES  111-120  39 

ing  water  with  hot  iron,  and  where  oxygen  and  hydrogen  are  obtained 
by  decomposing  water  by  the  electric  current. 

•  11.  See  Section  108,  p.  108.  Other  illustrations  of  the  law  of  mul- 
tiple proportions  are  carbon  monoxide  and  carbon  dioxide,  Section 
66,  p.  64,  and  in  Section  71,  p.  69,  it  is  stated  that  there  are  several 
distinct  compounds  of  nitrogen  and  oxygen.  The  law  of  multiple 
proportions  as  stated  in  Section  66  would  embrace  these  oxides  of 
nitrogen. 

12.  See  Section  108,  p.  108. 

13.  Hydrogen  peroxide  destroys  germs  because  it  oxidizes  them. 
It  is  not  a  case  of  complete  combustion,  as  for  example  when  wood 
burns.     But  some  of  the  many  chemical  substances  within  the 
little  germ  cell  which  are  essential  to  its  life  processes  are  oxidized, 
and  thus  indirectly  the  germ  is  destroyed.     The  hydrogen  peroxide 
is  a  poison  for  the  germ,  just  as  arsenic,  prussic  acid,  or  corrosive 
sublimate,  are  poisons  for  human  beings.     These  poisons  do  not 
disintegrate  the  whole  human  body,  but  they  do  interact  with  some 
one  or  other  of  the  chemical  substances  in  the  blood  or  tissues 
which  is  essential  to  the  delicately  balanced  chemical  processes  of 
the  body. 

14.  Hydrogen  can  hold  oxygen  very  firmly  bound  in  water,  so 
that  water  is  a  very  stable  substance ;  but  the  extra  quantity  of  oxy- 
gen in  hydrogen  peroxide  is  just  barely  held  there  under  favorable 
conditions.     It  is  ready  to  break  away  on  the  least  excuse,  and  it 
thus  happens  that  readily  oxidizable  bodies  like  the  skin  and  cotton 
are  vigorously  attacked  by  this  oxygen  from  the  hydrogen  peroxide, 
even  though  they  remain  quite  unaffected  by  the  oxygen  of  the  at- 
mosphere at  ordinary  temperatures. 


CHAPTER  XI 

HYDROGEN 

Pages  111-120 

As  hydrogen  was  first  discovered  by  the  pupil  while  decom- 
posing water,  it  is  a  most  natural  thing  to  make  next  a  study  of  its 


40  HYDROGEN 

preparation,  properties,  and  uses.  This  is  done  in  Chapter  XL 
After  connecting  the  preparation  of  hydrogen  with  the  displacing 
of  the  element  from  water  by  means  of  active  metals,  we  next  sug- 
gest a  series  of  experiments  to  be  performed  by  the  pupils  with 
various  dilute  acids  and  various  metals  capable  of  displacing  hydro- 
gen from  them. 

Iron,  zinc,  and  then  magnesium  may  be  used  with  dilute  sul- 
phuric acid,  and  then  hydrochloric  acid,  in  test  tube  quantities. 
The  hydrogen  produced  can  be  lighted  at  the  mouth  of  the  tube. 
Various  fruit  acids,  such  as  citric  and  tartaric,  may  be  tested  with 
bits  of  magnesium.  Acetic  acid,  cream  of  tartar  solution,  and  sour 
milk  may  be  similarly  tested  by  some  of  the  pupils  to  show  that  all 
the  common  acids  contain  replaceable  hydrogen,  which  is  dis- 
placed by  certain  active  metals.  Copper,  silver,  gold,  and  plati- 
num may  be  briefly  tried  by  members  of  the  class  to  add  the  in- 
formation that  certain  metals  fail  to  displace  hydrogen  from  acids. 

In  the  classroom  or  in  the  laboratory,  a  brief  study  of  the  pro- 
portions of  hydrogen  and  air  which  give  the  sharpest  explosion, 
may  be  made.  This  work  can  be  related  to  both  the  two  to  one  vol- 
ume relation  of  hydrogen  and  oxygen  in  water  and  to  the  one  to  four 
relation  of  oxygen  and  nitrogen  in  air.  Thus  a  mixture  having 
two  volumes  hydrogen  with  five  of  air  would  have  two  volumes 
hydrogen  to  one  volume  oxygen  and  hence  give  the  sharpest 
explosion.  The  practical  bearing  of  this  matter  on  explosions 
due  to  gas  leaks  should  then  be  brought  out  and  the  danger  of  a 
relatively  small  leak  shown.  In  the  latter  case,  there  will  always 
be  enough  oxygen  present  to  completely  burn  what  gas  is  pres- 
ent, while  in  case  of  the  presence  of  excess  of  gas  a  much  milder 
explosion  might  result.  The  explosive  character  of  a  mixture  of 
illuminating  gas  and  air  may  be  shown  to  a  class  by  the  teacher,  us- 
ing a  250  c.c.  Erlenmeyer  flask  with  about  one  volume  of  gas  to  five 
or  six  volumes  of  air.  The  flask  should  be  wrapped  in  a  towel 
when  the  mixture  is  lighted.  Usually  the  sharpest  explosion  that 
can  be  had  with  illuminating  gas  and  air  is  very  tame  and  cannot 
be  shown  in  a  test  tube.  It  requires  the  confinement  that  a  flask 
with  wide  body  and  narrow  neck  affords.  The  explosive  character 
of  gasoline  vapor  mixtures  with  air  should  be  touched  upon,  and 


PAGES  111-120  41 

pupils  should  be  made  acquainted  with  the  necessary  precautions 
for  preventing  such  explosions. 

The  oxyhydrogen  and  oxyacetylene  blowpipes  deserve  some 
attention  at  this  point,  and  the  latter  type  is  now  so  widely  used 
that  a  visit  may  be  made  to  some  plant  that  makes  use  of  it.  The 
intense  heat  developed  and  the  ease  with  which  iron  and  other 
refractory  materials  may  be  melted,  will  interest  pupils  greatly.  If 
no  such  place  is  available,  the  pupils  can  be  given  some  under- 
standing of  the  principle  involved  by  showing  them  a  blast  lamp  or 
even  a  double  tube  blowpipe.  If  specimens  of  the  scientific  rubies 
and  sapphires  which  are  made  with  the  oxyhydrogen  blowpipe  are 
available,  much  interest  will  be  awakened  in  the  pupils'  minds. 
Any  jeweler  will  probably  lend  a  few  specimens  for  class  study. 
For  a  good  account  of  the  method  of  manufacture  see  the  Outlook 
of  March  22,  1913. 

The  subject  of  reduction,  especially  the  use  of  hydrogen  as  a  re- 
ducing agent,  should  be  dwelt  upon  sufficiently  here,  so  that  it  may 
be  recalled  later  when  a  deeper  study  of  it  must  be  made.  See 
Sections  256,  387,  and  391,  pp.  241,  364,  and  368. 

Gaseous  fuels  should  also  receive  a  bit  of  classroom  attention,  so 
that  their  nature  and  relation  to  hydrogen  shall  not  be  entirely  un- 
known when  taken  up  later  in  Sections  283,  284,  and  285,  pp.  270- 
275. 

Answers  to  Questions  on  Chapter  XI 
Page  119 

1.  See  Section  109,  p.  111. 

2.  Oxygen  has  a  strong  chemical  attraction  for  hydrogen,  as  is 
evidenced  by  the  violence  with  which  the  two  elements  unite  in  the 
formation  of  water.     This  chemical  attraction  has  to  be  overcome 
to  separate  the  hydrogen  from  water,  and  this  may  be  accomplished 
by  using  some  substance,  for  example,  iron  (Section  100,  p.  100), 
sodium   (Section   101,   p.    102),   or    zinc    (Section    102,   p.    103), 
which  has  a  still  stronger  chemical  attraction  for  oxygen  than  has 
hydrogen.     It  may  also  be  accomplished  by  bodily  tearing  apart 
the  two  elements  by  some  force  stronger  than  their  force  of  attrac- 


42  HYDROGEN 

tion.     Such  a  force  can  be  supplied  by  an  electric  current  (Section 
103,  p.  103). 

3.  Since  sodium  can  decompose  water  and  liberate  hydrogen,  it  is 
obvious  that  sodium  must  have  the  stronger  attraction  for  the  oxygen. 

4.  See  Section  111,  p.  112. 

5.  Hydrogen  can  be  distinguished  from  the  colorless,  odorless 
gases  oxygen  and  nitrogen  in  that  it  burns.     It  can  be  distinguished 
from  carbon  monoxide  in  that  water  can  be  condensed  if  the  products 
of  combustion  pass  over  a  cold  surface.     But  there  are  numerous 
colorless,  odorless  gases  composed  of  carbon  and  hydrogen  which 
burn  and  yield  water  vapor.     Their  combustion  products,  however, 
would  cloud  lime  water,  due  to  the  presence  of  the  carbon  dioxide. 

6.  See  Section  115,  p.  114. 

7.  The  flame  of  hydrogen  burning  in  air  is  less  hot  than  that  of 
hydrogen  burning  in  oxygen,  because  of  the  inert  nitrogen,  which 
absorbs  some  of  the  heat  and  thus  lowers  the  temperature. 

8  and  9.   See  Section  124,  p.  118. 

10.  In  a  properly  adjusted  gas  stove  the  gaseous  fuel  comes  into 
contact  with  a  sufficient  amount  of  air  for  complete  combustion. 
Furthermore,  the  flame  is  very  hot,  and  before  any  of  the  fuel  can  es- 
cape from  the  high  temperature  region  of  the  flame,  it  has  been  com- 
pletely consumed. 

11.  The  kindling  temperature  of  gas  is  rather  high,  —  at  least 
a  temperature  at  which  a  solid  substance  would  glow  with  a  dull  red 
color.     The  heat  of  the  flame  decomposes  the  hydrogen  and  carbon 
compounds  into  the  free  elements.     The  solid  particles  of  carbon 
(soot)  become  incandescent  and  give  luminosity  to  the  flame.     If 
any  part  of  this  mixture  can  escape  from  the  hot  part  of  the  flame 
before  it  comes  in  contact  with  sufficient  oxygen  for  its  combustion, 
it  will  be  chilled  and  produce  smoke.     As  we  know,  it  is  not  difficult 
to  make  a  gas  flame  smoke  if  the  supply  of  air  is  partially  shut  off. 
If  one  holds  a  piece  of  cold  metal  in  an  otherwise  smokeless  flame, 
soot  is  deposited  on  the  metal,  because  some  of  the  glowing  carbon 
particles  are  cooled  below  their  kindling  temperature. 

12.  Since  copper  oxide  is  reduced  to  metallic  copper  (Section  123, 
p.  118)  by  heating  in  a  current  of  hydrogen,  it  would  not  be  unrea- 
sonable to  suppose  that  rust  (iron  oxide)  might  also  be  reduced  to 


PAGES  111-120  43 

metallic  iron  by  heating  in  hydrogen.  This  can  actually  be  accom- 
plished. However,  we  may  recall  the  process  of  obtaining  hydro- 
gen by  passing  steam  over  hot  iron  (Section  100,  p.  100).  If  it  is 
possible  for  iron  to  withdraw  oxygen  from  its  compound  with  hydro- 
gen, is  it  not  a  contradiction  if  hydrogen  can  withdraw  oxygen  from 
iron  oxide  and  leave  metallic  iron?  This  seeming  discrepancy  can 
be  explained  as  follows  : 

Hydrogen  and  iron  have  somewhere  nearly  the  same  attraction  for 
oxygen.  So  if  hydrogen  is  passed  over  hot  iron  oxide,  it  may  wrest  a 
little  of  the  oxygen  from  the  iron.  The  iron  might  perhaps  be  able 
to  get  back  this  oxygen  from  the  water  vapor  except  that  .the  latter 
is  swept  on  out  of  the  way  by  the  current  of  fresh  hydrogen  passing 
through  the  tube.  Thus  the  iron  oxide  can  be  reduced  little  by  little 
until  it  is  all  reduced,  because  the  water  vapor  as  fast  as  formed  is 
swept  out  of  the  way  where  it  cannot  reverse  the  reaction.  But 
when  steam  is  passed  over  heated  iron,  the  latter  can  withdraw  a 
little  oxygen,  and  the  hydrogen  so  liberated  is  swept  out  of  the  way 
by  the  current  of  steam.  Thus  gradually  the  metallic  iron  may 
all  become  changed  to  oxide,  if  the  hydrogen  formed  is  continually 
swept  away  and  thus  prevented  from  again  reducing  the  iron  oxide. 

13.   Weight  of  iron  oxide       ........     5.8446  grams 

Weight  of  iron        ......     ....     5.1300  grams 

Weight  of  oxygen  combined     ......     0.7146  gram 

.Combining  ratio  by  weight  of  oxygen  to  hydrogen  =  7.94:  1.00 
(see  Section  107,  p.  107). 

Let  x  =  weight  of  hydrogen  liberated. 

Then  0.7146  :  x  ::  7.94  :  1.00 

x  =  0.090  =  weight  of  hydrogen  in  grams. 

But  weight  of  one  liter  of  hydrogen  (standard  conditions)  =  0.09 
gram  (see  Appendix,  p.  428). 

0  OQO 

.*.  Volume  of  hydrogen  (standard  conditions)  =  -~r    =  1  00  liter. 


14.    11.2  liters  hydrogen  (standard  conditions)  weigh  11.2  X  0.09 

=  1.008  grams. 
1.008  grams  hydrogen  combine  with  7.94  X  1.008  =  8.004 

grams  of  oxygen. 
Weight  of  water  formed  =  1.008  +  8.004  =  9.012  grams. 


44  THE  ATOMIC  THEORY 

CHAPTER  XII 

THE   ATOMIC    THEORY 

Pages  121-128 

THE  atomic  theory  is  approached  through  the  laws  of  definite 
and  multiple  proportions,  which  led  Dalton  to  advance  the  theory. 
The  presentation  of  the  theory  is  made  more  vivid  to  the  pupil 
by  the  use  of  a  figurative  example,  that  of  the  beans  and  peas. 
The  pupil  will  usually  be  found  quite  eager  to  use  his  imagination 
in  connection  with  chemical  theory,  if  at  all  encouraged  to  do  so. 
Some  bright  pupils  will  even  devise  an  equivalent  for  Avogadro's 
theory,  if  led  to  consider  matter  from  the  standpoint  of  the  kinetic 
theory.  The  children  of  to-day,  like  those  early  speculators  in  the 
childhood  of  the  race,  make  very  good  "  atomists."  In  order  not  to 
give  too  much  of  this  sort  of  material  at  one  time,  and  also  in  order 
to  acquire  more  facts  to  be  considered  in  the  light  of  the  atomic 
theory,  the  chapter  on  hydrogen  chloride  is  next  introduced. 

Answers  to  Questions  on  Chapter  XII 

Page  128 

1.  Dalton's  atomic  theory  was  based  on  the  two  groups  of  facts 
which  are  summarized  in  the  laws  of  definite  and  multiple  propor- 
tions respectively. 

2.  See  Section  126,  p.  122. 

3.  See  Section  127,  p.  122. 

4.  Charcoal  is  a  mass  consisting  of  countless  atoms  of  carbon 
which  are  held  firmly  together  by  some  rather  mysterious  force  of 
cohesion.     Charcoal  begins  to  burn  in  air  or  in  oxygen  only  at  a 
high  temperature.     We  may  suppose  that  the  heat  loosens  the  cohe- 
sion of  the  carbon  atoms  for  each  other,  making  it  possible  for  two 
oxygen  atoms  to  come  into  closer  contact  with  each  carbon  atom. 
The  attraction  of  oxygen  atoms  for  carbon  atoms  is  apparently 
far  greater  than  the  cohesion  of  the  carbon  atoms  to  each  other.     In 
fact,  the  attraction  is  so  great  that  the  atoms  in  flying  together  gen- 


PAGES   129-140  45 

crate  heat,  thereby  raising  the  temperature  still  more  and  making 
the  reaction  self-sustaining.  In  the  molecules  of  carbon  dioxide 
apparently  nearly  all  of  the  cohesive  force  of  the  carbon  atoms 
is  used  up  in  holding  the  oxygen  atoms  in  combination.  There 
is  little  cohesion  among  the  molecules  of  carbon  dioxide,  and  its 
molecules  therefore  remain  widely  separated  as  a  gas. 

5.  It  has  been  suggested  that  in  water  two  hydrogen  atoms  are 
attached  to  one  oxygen  atom  in  the  molecule  (last  paragraph,  Sec- 
tion 128,  p.  125).     We  know  that  hydrogen  peroxide  contains  for  a 
given  weight  of  hydrogen  exactly  twice  as  much  oxygen  as  does 
water  (fourth  paragraph,  p.  109).     Or  in  other  words,  for  a  given 
weight  of  oxygen,  hydrogen  peroxide  contains  only  one  half  as  much 
hydrogen  as  does  water.     If  then  the  molecule  of  water  contains 
two  atoms  of  hydrogen  and  one  of  oxygen,  the  simplest  supposition 
is  that  the  molecule  of  hydrogen  peroxide  contains  one  atom  of  hy- 
drogen and  one  atom  of  oxygen. 

It  may  be  stated  here  that  there  are  good  reasons  for  believing  that 
the  molecule  of  hydrogen  peroxide  contains  two  atoms  each  of  hy- 
drogen and  oxygen,  although  no  reason  has  been  brought  forward 
yet  in  the  textbook  for  holding  such  a  view. 

6.  See  Section  130,  p.  126. 


CHAPTER  XIII 

HYDROGEN    CHLORIDE 

Pages   129-140 

THE  pupil  will  usually  be  given  an  opportunity  to  prepare  both 
hydrogen  chloride  and  its  water  solution,  and  to  study  the  properties 
of  both.  The  uses  can  best  be  taken  up  in  the  classroom  after 
reference  books  have  been  consulted.  The  rather  detailed  explana- 
tion of  methods  for  finding  the  volume  composition  of  hydrogen 
chloride  is  intended  to  amplify  the  somewhat  similar  study  of  water 
in  Chapter  X,  and  to  afford  material  for  use  in  connection  with  the 
following  chapter  on  Avogadro's  hypothesis.  It  thus  leads  toward 
the  establishing  of  the  formula  HC1. 


46  HYDROGEN   CHLORIDE 

Answers  to  Questions  on  Chapter  XIII 

Page  140 

1.  See  Sections  133,  134,  and  137,  pp.  129,  130,  and  133. 

2.  See  Section  140,  p.  135. 

3.  See  Section  141,  p.  136. 

4.  See  Sections  133,  135,  and  136,  pp.  129,  130,  and  132. 
6.  See  Section  136,  p.  132. 

6.  See  Section  138,  p.  133. 

7.  Pressure  of  chlorine  =  20  cm. 
Pressure  of  hydrogen  =  76  -  20  =  56  cm. 

20  cm.  of  chlorine  react  with  20  cm.  of  the  hydrogen,  forming 
hydrogen  chloride,  with  a  pressure  of  40  cm.,  and  leaving  hydrogen 
with  a  pressure  of  36  cm.  After  explosion  total  pressure  is  40  +  36 
=  76  cm. 

8.  If  water  enters  the  tube,  all  of  the  hydrogen  chloride  is  dis- 
solved and  only  the  hydrogen  is  left.     The  pressure  of  this  gas  in 
the  100  c.c.  tube  was  36  cm.,  or  in  other  words  at  a  pressure  of  36  cm. 
the  volume  was  100  c.c.     Now  with  the  pressure  increased  to  76  cm., 
the  volume  decreases  in  inverse  ratio : 

new  volume  =  100  X  ^  =  47.4  c.c. 

9.  To  solder  metals,  heat  is  necessary  to  melt  the  solder.     At 
the  higher  temperature  a  film  of  oxide  forms  over  the  surfaces  of  the 
metals  as  well  as  of  the  solder.     This  prevents  the  solder  from  ad- 
hering.    Muriatic  acid  reacts  with  and  removes  this  film  of  oxide 
and  so  allows  the  solder  to  come  into  contact  with  the  clean  metal 
and  adhere. 

10.  One  reason  that  less  hydrochloric  acid  than  sulphuric  acid 
is  used  in  the  arts  is  that  it  costs  more.     Another  important  reason 
is  that  the  most  concentrated  solution  of  hydrochloric  acid  contains 
but  40  %  of  the  acid,  whereas  concentrated  sulphuric  acid  as  prepared 
is  about  98  %  acid.     In  shipping  the  acid  from  the  chemical  works 
to  the  point  where  it  is  used,  the.  cost  of  freight  on  the  60  %  of  water 
in  the  hydrochloric  acid  is  by  no  means  a  negligible  item. 

For  a  number  of  purposes,  the  fact  that  sulphuric  acid  is  non- 
volatile gives  it  the  preference  over  hydrochloric  acid. 


PAGES   141-146  47 

CHAPTER  XIV 

AVOGADRO'S   THEORY 

Pages  141-146 

FOLLOWING  the  historical  order  of  events,  Chapter  XIV  leads  up  to 
Avogadro's  theory  through  Gay  Lussac's  law.  It  is  strongly  recom- 
mended that  the  teacher  read  to  the  class  at  this  point  the  following 
translations  from  the  original  papers  of  Gay  Lussac  and  Avogadro, 
as  giving  in  a  clearer  fashion  than  most  textbooks  present  them, 
the  facts  and  deductions  from  the  facts,  of  those  great  scientists. 

Quotation  from  the  original  memoirs  of  Gay  Lussac  upon  the 
combining  volumes  of  gases  : * 

"  Thus  it  appears  to  me  evident  that  all  gases  in  reacting  with 
each  other  always  combine  in  the  simplest  proportions;  and  we 
have  indeed  seen  in  the  preceding  examples  that  the  proportion  of 
combination  is  that  of  one  to  one,  of  one  to  two,  or  of  one  to  three. 

"It  is  very  important  to  observe  that  when  one  considers  the 
weights  there  is  no  simple  and  finished  proportion  between  the  ele- 
ments of  a  primary  combination :  it  is  only  when  there  is  a  second 
compound  between  the  same  two  elements  that  the  new  proportion 
of  the  element  which  has  been  added  is  a  multiple  of  the  first  amount. 
Gases,  on  the  contrary,  in  whatever  proportion  they  may  combine,  al- 
ways give  rise  to  compounds  of  which  the  elements  are  multiples 
of  each  other  in  volume. 

"  Not  alone  do  gases  combine  among  themselves  in  very  simple 
proportions  as  we  have  just  seen,  but  further,  the  apparent  contrac- 
tion in  volume  which  they  experience  as  a  result  of  the  combination 
has  also  a  simple  relation  with  the  volumes  of  the  gases,  or  rather 
with  that  of  one  of  them." 

Quotation  from  the  original  Essay  of  A.  Avogadro : 2  "  M.  Gay 

1  Memoirs  de   la  Societe  d'Orcueil,  Vol.  II,  p.  207  (1809).     Translated 
from    a  copy  in  Les    Classiques  de   la  Science,    Librairie    Armand    Colin, 
Paris,  1913. 

2  First  published  in  the  Journal  de  Physique  de  Delametherie  in    1811. 
Translation  made  from  Les  Classiques  de  la  Science,  Librairie  Armand  Colin, 
Paris,  1913. 


48  AVOGADRO'S  THEORY 

Lussac  has  shown  in  a  very  interesting  memoire  that  the  combinations 
of  gases  among  themselves  always  take  place  according  to  very 
simple  volume  relations  and  that  when  the  product  of  the  combina- 
tion is  gaseous  its  volume  is  also  in  very  simple  relation  with  those 
of  its  constituents;  but  the  proportions  of  the  quantities  of  sub- 
stances entering  into  combinations  would  appear  to  depend  only 
upon  the  relative  numbers  of  the  molecules  which  combine,  and  of 
the  number  of  compound  molecules  which  result  from  the  combina- 
tion. 

"  We  must  then  admit  that  there  are  also  very  simple  relations 
between  the  volumes  of  gaseous  substances  and  the  number  of  mole- 
cules, whether  simple  or  compound,  which  go  to  make  them  up. 

"  The  first  hypothesis  which  presents  itself  in  this  case,  and  indeed 
the  only  admissible  one,  is  to  suppose  that  the  number  of  gas  parti- 
cles in  any  gas  whatever  is  always  the  same  in  equal  volumes,  or  is 
always  proportional  to  the  volumes.  In  truth,  if  one  should  suppose 
that  the  number  of  particles  in  a  given  volume  was  different  for 
different  gases,  it  would  scarcely  be  possible  to  conceive  that  the 
law  which  would  then  preside  over  the  distance  between  the  particles 
could  give  in  every  case  relations  as  simple  as  the  facts  which  we 
have  just  cited  oblige  us  to  admit  between  the  volume  and  the  num- 
ber of  particles. 

"Starting  with  this  hypothesis,  we  see  that  we  have  the  means  of 
very  easily  determining  the  relative  masses  of  the  molecules  of  bodies, 
which  we  may  have  in  the  gaseous  condition,  and  the  relative  num- 
ber of  molecules  in  compounds;  for  the  relations  of  the  masses 
of  the  molecules  are  then  the  same  as  those  of  the  densities  of  the 
gases  at  like  pressure  and  temperature,  and  the  relative  num- 
ber of  molecules  in  a  compound  is  given  immediately  by  the  rela- 
tion of  the  volumes  of  the  gases  which  form  it." 

The  presentation  of  the  argument  based  on  Avogadro's  theory 
and  the  facts  of  Gay  Lussac's  law,  that  the  molecules  of  the  com- 
mon elementary  gases  must  be  at  least  double,  is  given  in  some  de- 
tail, as  this  argument,  while  simple  enough  to  advanced  students, 
is  always  difficult  for  the  beginner  to  understand.  It  will  pay  to  go 
over  and  over  it  with  different  examples  until  the  pupils  all  really 
comprehend  it. 


PAGES   141-146  49 

The  following  questions  may  help  to  fix  this  work : 

1.  One  volume  of  nitrogen  unites  with  three  volumes  of  hydrogen, 
yielding  two  volumes  of  ammonia  gas.     What  are  the  relative  num- 
bers (in  lowest  terms)  of  the  particles  of  each  of  the  gases  according 
to  Avogadro's  hypothesis  ? 

2.  In  the  above  case  show  that  each  nitrogen  particle  must  be 
at  least  double. 

3.  Explain  why,  in  the  above  case,  the  argument  as  to  the  double- 
ness  of  hydrogen  particles  is  not  as  direct. 

4.  Two  volumes  of  nitrogen  unite  with  one  volume  of  oxygen, 
forming  two  volumes  of  nitrous  oxide.     Draw  a  graph  (using  the 
symbol  Q  for  a  nitrogen  molecule  and  the  symbol  $  for  an  oxygen 
molecule)  showing  what  must  have  taken  place  during  the  reaction. 

Answers  to  the  above   Questions 

1.  The  relative  numbers  of  particles  are  as  follows  :  one  nitrogen 
particle  unites  with  three  hydrogen  particles  to  form  two  ammonia 
gas  particles.     This  is  true  because  of  Avogadro's  hypothesis  which, 
in  addition  to  asserting  that  equal  volumes  of  all  gases  under  like 
conditions  have  equal  numbers  of  gas  particles,  also  goes  on  to  as- 
sert that  where  the  volumes  are  not  equal  the  numbers  of  particles 
are  strictly  proportional  to  the  volumes. 

2.  In  the  case  just  discussed,  the  nitrogen  gas  particles  must  con- 
tain at  least  two  atoms  each  for  the  following  reasons : 

Let  x  =  the  number  of  gas  particles  per  unit  volume  of  any  of 
the  gases. 

Then  we  have  x  particles  of  nitrogen, 

and  2  x  particles  of  ammonia. 

But  every  one  of  the  2  x  particles  of  ammonia  has  at  least  one 
nitrogen  atom  in  it  (for  all  ammonia  has  nitrogen  in  it). 

Hence,  as  we  have  2  x  ammonia  particles  with  at  least  1  nitrogen 
atom  each,  we  have  at  least  2  x  nitrogen  atoms  in  our  ammonia. 
But  we  had  only  1  x  nitrogen  gas  particles  to  start  with.  Hence 
every  one  of  these  must  have  been  at  least  double. 

3.  The  same  argument  as  to  the  doubleness  of  hydrogen  gas 
particles  cannot  be  made  because  the  number  of  new  (ammonia) 


50 


ATOMIC  AND   MOLECULAR  WEIGHTS 


particles  must  be  less  (by  Avogadro's  hypotheses)  than  the  number 
of  hydrogen  particles  with  which  we  started  (since  the  volume 
is  less).  Hence  we  have  no  chance  to  show  the  presence  of 
hydrogen  in  more  particles  than  at  first.  There  is  indicated  rather 
a  condensation  of  hydrogen  particles. 

However,  it  is  true  that  3  volumes  of  hydrogen  disappear  in  the 
formation  of  2  volumes  of  ammonia.  If  then  we  are  sure  that  only 
a  single  new  substance  is  formed,  it  is  obvious  that  3  atoms  cannot 
be  divided  into  two  equal  parts  without  splitting  an  atom,  and  we 
thus  have  proof  that  3  molecules  of  hydrogen  contain  at  least  6 
atoms. 


4. 


Indicating  that  during  the  reaction  that  forms  nitrous  oxide, 
each  oxygen  molecule  must  have  divided  into  two  atoms,  one  of 
which  joined  a  molecule  of  N2  and  the  other  joined  another  N2 
molecule,  thus  forming  2  molecules  of  N20  (nitrous  oxide) . 

Sections  148-152,  pp.  144-146,  may  perhaps  be  omitted  with 
young  pupils  or  where  time  is  lacking.  Older  pupils  will,  however, 
appreciate  the  light  that  is  shed  on  Boyle's  and  Charles'  laws  in 
these  paragraphs. 


CHAPTER  XV 

ATOMIC   AND    MOLECULAR    WEIGHTS 

Pages  147-163 

THE  subject  matter  of  this  chapter  is  always  difficult  of  compre- 
hension by  high  school  pupils.  No  attempt  has  been  made  to  handle 
the  question  of  how  atomic  weights  are  obtained  in  any  full  fashion. 
One  example  has  been  made  to  suffice,  that  of  the  obtaining  of  the 
atomic  weight  of  copper,  and  even  here,  the  matter  of  hqw  it  is 
decided  that  copper  and  oxygen  are  present  atom  for  atom  has  been 
passed  over  with  the  mere  announcement  that  it  has  been  so  decided. 


PAGES   147-163  51 

It  is  questionable  whether  it  will  pay  to  attempt  to  go  more  deeply 
into  the  subject  with  high  school  pupils  than  has  been  done  in  this 
chapter. 

In  the  case  of  gram-molecular  volume,  the  explanation  has  been 
made  more  thorough.  It  is  believed  that,  with  the  older  pupils  at 
least,  it  is  possible  by  this  complete  treatment  to  make  them  under- 
stand why  22.4  liters  were  chosen  and  why  it  is  that  the  weight  of 
that  volume  of  any  gas  at  standard  conditions  is  numerically  equal 
to  the  molecular  weight. 

Use  is  at  once  made  of  this  method  of  finding  molecular  weights, 
and  the  weights  thus  found  are  at  once  applied  in  deciding  final 
formulas,  Section  168,  p.  160.  The  weight  significance  of  formulas 
is  driven  home,  Sections  162,  163,  164,  pp.  154-156,  and  the  subject 
of  equations  is  then  studied.  Many  textbooks  and  many  teachers 
have  introduced  equations  far  earlier  than  this  in  the  chemistry 
course,  but  their  use  by  pupils  who  do  not  and  cannot  comprehend 
their  meaning  or  their  origin  is  to  be  deprecated.  It  is  better  to 
wait  until  the  right  to  use  them  has  been  earned.  It  will  be  well  to 
give  the  class  a  good  drill  at  this  point  in  the  balancing  of  equations. 
They  should  first  of  all  be  reminded  that  equations  cannot  be  "  made 
up  "  without  experimental  facts,  and  that  in  every  case  they  are 
supposed  to  represent,  in  a  species  of  shorthand,  what  has  been 
found  out  to  be  true  in  the  particular  case  under  consideration.  It 
may  be  announced,  however,  that  so  much  experience  has  now  ac- 
cumulated that  we  can  in  many  cases  tell  in  advance  what  is  likely  to 
be  the  result  of  putting  together  certain  substances,  and  that  one  with 
a  considerable  knowledge  of  chemistry  can  write  equations  offhand 
with  some  likelihood  of  correctly  expressing  results.  A  preliminary 
hint  as  to  the  numerical  combining  habit  of  the  atoms  of  the  ele- 
ments as  compared  with  the  combining  habit  of  hydrogen  atoms 
(i.e.  valence)  may  be  given  here.  Pupils  may  then  be  given  exer- 
cises, first  in  looking  up,  in  the  reference  books,  equations  for  reac- 
tions that  have  already  become  familiar  to  them,  and  second, 
in  completing  and  balancing  incomplete  or  unbalanced  equations. 

From  this  point  on,  every  pupil  should  be  required  to  look  up  and 
write  the  equations  for  all  reactions  taking  place  in  the  laboratory 
and  lecture  table  work,  provided  the  reactions  are  well  understood. 


52  ATOMIC  AND  MOLECULAR  WEIGHTS 

Too  much  time  may  easily  be  spent  in  balancing  equations.  The 
value  of  this  species  of  exercise  is  frequently  overestimated.  Like 
the  clerk  in  Chaucer's  Prologue  who  "  seemed  busier  than  he  was," 
the  pupil  who  can  readily  complete  or  balance  equations  may  really 
be  accomplishing  very  little.  An  understanding  of  what  equations 
are  and  how  they  are  derived,  and  the  ability  to  grasp  the  story 
conveyed  by  them  is  of  far  more  value  to  the  pupil  than  any  artifi- 
cial facility  in  making  the  two  sides  balance. 

The  introduction  of  the  few  paragraphs  on  ozone  at  the  end  of 
this  chapter  permits  the  practical  application  of  what  has  just  been 
gained,  as  the  determination  of  the  molecular  formula  of  ozone  de- 
pends upon  the  use  of  the  molal  volume  method.  Incidentally  the 
properties  of  the  substance  are  described  and  its  uses  touched  upon. 
The  extensive  European  use  of  ozone  as  a  means  of  purifying  munici- 
pal water  supplies  should  be  enlarged  upon  by  the  teacher.  Pos- 
sibly a  little  ozone  may  be  prepared  by  the  teacher,  using  some 
freshly  scraped  yellow  phosphorus.  This  should  be  placed  in  the 
bottom  of  a  large  wide-mouth  bottle  and  half  covered  with  water 
to  prevent  its  ignition.  Starch-iodide  paper  may  then  be  moistened 
and  lowered  into  the  flask  to  show  the  oxidizing  action  of  ozone, 
and  a  typical  test  for  it,  and  the  pupils  should  be  allowed  to  smell 
of  it. 

Degree  of  Precision  in  Problem  Work 

In  ordinary  chemical  arithmetic  the  accuracy  obtained  with  a 
slide  rule  or  a  four-place  logarithm  table  is  sufficient.  This  gives 
the  result  with  an  accuracy  of  about  one  part  in  1000.  It  is  need- 
less to  express  atomic  weights  as  used  in  calculations  with  any  greater 
accuracy.  For  example : 

H  =  1.008.  To  drop  the  8  in  the  last  place  would  be  neglecting 
T^nnr,  or  nearly  rihy  of  the  whole,  which  would  not  be  allowable. 
Therefore  use  atomic  weight  1.008". 

Cl  =  35.46.  To  round  off  this  number  to  35.5  would  be  adding 
Tr&tf,  or  approximately  nfar,  which  is  allowable.  Therefore  round 
off  chlorine  to  35.5. 

HC1  =  1.008  +  35.46  =  36.468.     Round  off  to  36.5. 

Ba  =  137.37.     Round  off  to  137.4. 


PAGES  147-163  53 

It  should  be  remembered  that  a  result  is  accurate  only  to  the  same 
extent  as  the  least  accurate  quantity  which  is  used  in  the  multiplica- 
tions or  divisions  performed  in  obtaining  the  result.  Thus,  for 
example,  if  we  weigh  10  grams  of  sodium  chloride  on  a  balance  which 
may  be  in  error  by  as  much  as  1  gram,  we  have  a  possible  error  of  iV- 
If  we  calculate  from  this  that  by  adding  silver  nitrate  we  can  precipi- 

tate 

mol.  wt.  AgCl  107.88  +  35.46 

Xmol.  wt.  NaCl~        C   23.00  +  35.46 

=  24.51899  grams  of  AgCl, 

we  are  not  only  doing  needless  work  but  we  are  giving  a  wrong  im- 
pression, for  we  cannot  know  the  true  amount  to  nearer  than  yV,  or 
2.5  grams.  Therefore  round  off  the  answer  to  25  grams,  or  if  it  is 
wished  to  indicate  clearly  the  possible  error,  write  the  answer 
25  db  2.5  grams. 

It  is  very  difficult  to  get  the  pupil  to  grasp  the  idea  of  the  degree 
of  precision  of  his  measurements  and  results,  and  if  the  teacher 
were  to  insist  strongly  upon  it,  probably  very  little  time  would  be 
left  for  anything  else  in  the  course. 

At  least,  however,  the  teacher  may  be  careful  to  set  a  correct 
example  in  this  regard.  Provided  the  method  of  working  the  prob- 
lem is  correct,  answers  should  be  accepted  which  do  not  vary  from 
the  average  result  by  more  than  T7%?  of  the  value  of  the  result. 


Answers  to  Questions  on  Chapter  XV 

Page  163 

1.  0  =  16.00  g.  ;  H  =  1.008  g.  ;  01=  35.46  g.  ;   Na  =  23.00  g.  ; 
Fe  =  55.84  g. 

2.  H20  =  18.02  g.  ;         HC1  =  36.47  g.  ;         NH3  =  17.03  g.  ; 
N2  =  28.02  g.  ;  H2S04  =  98.09  g. 

3.  NaOH        +      HC1  -^  NaCl  +  H20 
23  +  16  +  1       1  +35.5 

40  36.5 

Let  x  =  the  weight  of  HC1  necessary. 
Then  40  :  36.5  :  :  40  :  x. 

x  =  36.5. 


54  ATOMIC  AND  MOLECULAR  WEIGHTS 

Therefore  36.5  grams  of  HC1  are  necessary. 

4.  36.5  g.  of  HC1  =  1  mole. 

Volume  of  1  mole  of  a  gas  (standard  conditions)  =  22.4  liters. 

22.4  liters,  answer. 

5.  From  equation  in  No.  3  we  see  that  one  mole  of  NaOH  yields 
one  mole  of  NaCl.     Since  we  started  with  1  mole  of  NaOH,  we  ob- 
tain 1  mole  of  NaCl,  or  23  +  35.5  =  58.5  grams. 

6.  BaCl2          +  H2S04        ->        BaS04  +  2  HC1 
137.4  +  2X35.5                          137.4  +  32.1+4x16 

208.4  233.5 

Let  x  =  weight  of  barium  sulphate. 
Then  208.4 :  233.5 : :  100 :  x. 

x  =  111.9  111.9  grams  =  weight  of  BaS04. 

7.  NaHC03  +  HC1  -+  C02        +  H20  +  NaCl 
84  grams  22.4  liters 

1  mole  of  NaHC03  yields  1  molal  volume  of  C02. 
Let  x  =  volume  of  C02. 
Then  84 :  22.4 : :  100 :  x. 

x  =  26.7  26.7  liters  =  weight  of  C02. 

8.  100  c.c.  of  ozonized  oxygen  becomes  102  c.c.  when  all  changed 
to  oxygen.     Gain  in  volume  due  to  change  of  ozone  to  oxygen 
=  2  c.c.     In  reaction  2  03  — >  3  02,  the  change  of  volume  =  ^  of 
the  volume  of  the  ozone. 

Volume  of  ozone  =  2  x  2  =  4  =  4  %  of  100. 
Therefore  4  %  by  volume  of  the  original  gas  was  ozone. 

9.  A  mole  of  ozone  =  3  X  16  =  48  grams. 

Volume  of  1  mole  of  ozone  under  standard  conditions  =  22.4  liters. 
Volume  of  1  gram  of  ozone  under  standard  conditions  =  -£g  X 
22.4  =  0.467  liter  =  467  c.c.     Answer,  467  c.c.  of  ozone. 

10.  92%  of  467  =  430  =  c.c.  of  ozone  changed. 

8%  of  467  =  37.4  =  c.c.  of  ozone  unchanged. 
430  c.c.  of  ozone  changes  to  f  X  430  =  645  c.c.  of  oxygen. 
Final  volume  =  645  +  37  =  682  c.c. 

11.  Volume  of  oxygen  changed  to  ozone  =  3  %  of  21  %  of  100  c.c. 
=  0.63  c.c.     This  contracts  by  £  of  its  volume  =  0.21  c.c.  when 
changed  to  ozone.     100  c.c.  of  air  contracts  0.21  c.c. 

12.  15.88  parts  by  weight  of  oxygen  are  combined  with  1  part  by 


PAGES   164-176  55 

weight  of  hydrogen  in  hydrogen  peroxide.  This  is  in  the  same  ratio 
as  16.00  parts  of  oxygen  and  1.008  parts  of  hydrogen.  But  these 
are  the  atomic  weights.  Therefore  hydrogen  peroxide  must  contain 
the  same  number  of  atoms  of  oxygen  and  hydrogen,  and  the  simplest 
formula  would  be  HO. 

13.  Hydrogen  peroxide  and  ozone  are  similar  in  their  properties 
in  that  they  are  both  unstable  and  give  off  oxygen  easily.  They  are 
capable  of  oxidizing  substances  even  when  dilute,  and  when  pure 
are  violent  oxidizing  agents,  as  well  as  being  explosive. 

CHAPTER  XVI 

CHLORINE 

Pages  164-176 

UNLESS  really  effective  down-draft  gas  hoods  are  available,  it  is 
probably  wiser  not  to  permit  pupils  to  prepare  chlorine  for  them- 
selves, on  account  of  the  exceedingly  irritating  and  even  dangerous 
character  of  this  gas.  Subsequent  effects  of  the  attack  upon  the 
mucous  surfaces  have  probably  been  underestimated  and  no  chances 
should  be  taken  in  such  matters.  Chlorine  is,  however,  so  typical  a 
non-metal  and  so  much  chemistry  can  be  learned  through  a  study  of 
it,  and  a  comparison  of  it  with  oxygen,  that  classes  should  all  be 
made  acquainted  with  it.  Where  proper  down-draft  hoods  are  not 
available,  a  good  way  for  the  teacher  to  do  in  preparing  chlorine  is 
to  set  up  a  generator  on  a  window  sill  where  there  is  strong  out  draft. 
Then  work  with  the  window  open  and  make  most  of  the  tests 
right  where  the  chlorine  is  generated.  The  use  of  solid  potassium 
permanganate  in  the  generator  as  an  oxidizing  agent  is  recommended 
because  of  its  convenience.  Concentrated  HC1  may  be  dropped 
upon  it  from  a  dropping  funnel,  or  lacking  the  funnel,  through  a 
thistle  tube  arranged  to  dip  beneath  the  contents  of  the  generator. 
Chlorine  can  thus  be  had  as  desired,  for  the  reaction  begins  promptly 
and  is  soon  over. 

Some  classroom  discussion  of  the  relative  activity  of  oxygen  and 
chlorine  will  be  needed  to  make  clear  the  fact  that  the  ease  with 


56  CHLORINE 

which  chlorine  begins  to  react  with  certain  elements  at  low  tem- 
perature is  not  a  fair  measure  of  its  activity.  The  practical  uses  of 
chlorine  deserve  considerable  classroom  discussion.  Bleaching 
powder  should  be  shown  in  its  ordinary  commercial  form,  and  some 
may  be  used  by  each  pupil  in  an  actual  bleaching  experiment  with 
ink  spots  or  bits  of  brightly  colored  calico. 

The  theory  of  chlorine  bleaching  can  best  be  approached  by  way 
of  the  well-known  reaction  between  chlorine  and  water.  Let  the  pupils 
know  of  the  actual  formation  of  hypochlorous  acid  in  this  reaction 
and  of  its  instability  and  the  consequent  loss  of  nascent  oxygen, 
when  it  is  heated,  when  the  sun  shines  on  it,  or  when  any  readily 
oxidized  substance  is  present  to  take  up  the  oxygen  as  fast  as  formed 
and  thus  prevent  reversal  of  the  reaction.  The  formation  of  hypo- 
chlorous  acid  from  bleaching  powder  can  then  be  explained  and  com- 
mercial bleaching  thus  connected  with  bleaching  by  means  of  chlo- 
rine water. 

Recent  improvements  in  the  commercial  process  eliminate  the 
use  of  sulphuric  acid  to  release  hypochlorous  acid.  The  bleacher 
prefers  to  depend  upon  the  slower,  but  safer,  action  of  carbonic 
acid  formed  from  the  C02  of  the  air.  This  reacts  with  the  soluble 
hypochlorites,  with  which  the  goods  are  first  moistened,  and  very 
slowly  liberates  the  unstable  hypochlorous  acid. 

If  possible,  a  steam  laundry  should  be  visited  and  the  method  of 
bleaching  studied.  Many  laundries  now  electrolyze  salt  solution, 
thus  getting  sodium  hypochlorite  to  use  as  a  bleaching  agent  instead 
of  calcium  hypochlorite. 

The  use  of  hypochlorites,  or  of  chlorine,  in  treating  suspected 
water  supplies  is  so  general  in  this  country  that  it  should  be  ex- 
plained. The  chemistry  is  very  similar  to  that  of  bleaching.  Some 
of  the  newer  plants  use  liquid  chlorine  for  this  purpose.  The  simi- 
larity between  this  use  of  chlorine  and  the  use  of  ozone  should  be 
pointed  out,  both  doing  the  work  by  the  formation  of  nascent  oxygen. 

Answers  to  Questions  on  Chapter  XVI 

Page  176 

1.  Sodium  chloride  is  the  chief  source  of  chlorine  in  nature.  Free 
chlorine  may  be  obtained  from  it  by  electrolysis,  or  by  treatment 


PAGES   164-176  57 

with  an  acid  and  an  oxidizing  agent,  for  example  sulphuric  acid 
and  manganese  dioxide. 

2.  See  Section  169,  p.  164. 

3.  See  (1)  Section  171,  p.  166  and  (2)  Sections  139  and  166,  pp. 
134  and  156. 

4.  See  Sections  173-176,  178,  180,  pp.  167-171. 

5.  Three  reasons  why  oxygen  may  be  considered  a  more  active 
non-metallic  element  than  chlorine  are :    (1)  In  Deacon's  process 
(Section  170,  p.   165),  oxygen  can  displace  chlorine  from  hydro- 
gen chloride.     (2)  A  mixture  of  hydrogen  and  oxygen  explodes 
with  more  violence  and  evolves  more  heat  than  a  similar  mixture 
of  hydrogen  and  chlorine  (Section  176,  p.   168).     Note:   The  heat 
evolved  in  the  respective  reactions  involving  the  molal  quantities 
indicated  is  as  follows  :    H2  +  ^  02  —>  H20  (vapor)  +  58,100  calo- 
ries ;     H2  +  C12  ->  2  HC1  (gas)  +  44,000    calories.     (3)  The   fact 
that  charcoal  and  fuels  containing  carbon  undergo,  when  once 
kindled,  a  rapid  self-sustaining  combustion  in  oxygen  but  not  in 
chlorine  can  also  be  taken  as  an  evidence  of  greater  activity  on  the 
part  of  oxygen.     Note :  A  number  of  facts  point  to  a  greater  activity 
on  the  part  of  chlorine,  e.g.  several  metals  combine  spontaneously 
with  chlorine  but  only  with  difficulty,  if  at  all,  with  oxygen.     There 
thus  does  not  seem  to  be  a  universal  standard  of  activity  for  the 
various  elements.     The  activity  varies  somewhat  according  to  the 
other  elements  which  are  concerned,  as  well  as  to  whether  the  system 
is  in  a  dry,  an  aqueous,  or  other  medium.     It  is  of  a  good  deal  of 
teaching  value,  however,  to  arrange  the  non-metals  in  an  order  cor- 
responding to  their  activity  and  to  note  that  the  order  is  at  least 
roughly  the  same  against  whatever  metallic  element  that  activity 
is  being  compared.     The  metals  also  may  be  arranged  in  the  order 
of  their  activity  (the  order  of   the  Electromotive  Series,  p.  329) 
and  the  order  is  practically  the  same  against  whatever  non-metal 
the  activity  is  being  considered. 

6.  Chlorine  is  used  practically  for  bleaching  (Section  180,  p.  170), 
as  a  germicidal  agent  (Section  184,  p.   174),  for  dissolving  gold 
(Section  178,  p.  170).     Note :  A  process  formerly  used  to  a  consider- 
able extent  in  extracting  gold  from  its  ores  was  to  treat  the  crushed 
ore  with  chlorine  and  then  dissolve  out  the  gold  chloride  with  water. 


58  SODIUM 

7.  See  Sections  180-182,  pp.  170-172. 

8.  4  HC1    +     Mn02  ->  MnCl2  +  2  H20  +  C12 
4  x  36.5       54.9  +  32 

146.0  86.9 

100  kilograms  of  36.5%  HC1  contain  36.5  kg.  of  HC1.  This  is  one 
kilogram  mole  of  the  substance.  We  see  from  the  equation  that  4 
moles  of  HC1  require  1  mole  of  Mn02.  One  kg.  mole  of  HC1  then 
will  require  £  kg.  mole  or  i  X  86.9  =  21.73  kg.  of  Mn02. 

9.  In  equation  in  No.  8  it  is  seen  that  4  moles  of  HC1  yield  1  mole 
of  C12.     Therefore  the  1  kg.  mole  actually  used  will  yield  J  kg. 
mole  =  1  X  71  =  17.75  kg.  of  C12. 

10.  The  I  kg.  mole  of  C12  obtained  in  No.  9  will  occupy  |  X 
22,400  =  5600  liters  or  5.6  cubic  meters. 

11.  4  HC1  +  Mn02  ->  2  H20  +  MnCl2  +  C12 
MnCl2  +  H2S04  ->  MnS04  +  2  HC1 

Adding  these  equations,  we  get 

2  HC1  +  H2S04  +  Mn02  ->  2  H20  +  MnS04  +  Cl, 
We  see  that  for  2  moles  of  HC1,  1  mole  of  C12  is  obtained  and  1 
mole  of  H2S04  and  1  mole  of  Mn02  are  needed. 
Therefore  for  1  kg.  mole  of  HC1  we  obtain  : 

i  kg.  mole  of  C12  =  }  X  71  =  35.5  kg.  of  C12, 
1  kg.  mole  of  H2S04  =  J  x  98.1  =  49.05  kg.  of  H2S04, 
i  kg.  mole  of  Mn02  =  |  X  86.9  =  43.45  kg.  of  Mn02. 

12.  To  obtain  chlorine  from  bleaching  powder  treat  it  with  sul- 
phuric acid,  which  first  reacts  to  set  free  the  two  acids  as  shown  : 
CaClOCl  +  H2S04  -+  CaS04  +  HC1  +  HC10  (Section  183,  p.  172). 
These  acids  then  react  with  each  other,  yielding  chlorine  (Section  180, 
p.  170). 


CHAPTER   XVII 

SODIUM 

Pages  177-191 

IF  experiments  are  performed  with  sodium,  it  must  be  remembered 
that  much  of  the  sodium  on  the  market  has  violently  explosive 


PAGES  177-191  59 

properties  when  reacting  in  any  considerable  quantity  with  water 
or  acids.  This  seems  to  be  due  in  part  to  the  presence  of  an  ex- 
plosive impurity  in  sodium  which  was  made  by  the  reaction  of 
highly  heated  carbon  with  sodium  hydroxide  in  the  electric  furnace. 
Teachers  cannot  be  too  careful  in  preventing  the  use,  by  pupils,  of 
pieces  of  sodium  larger  than  small  peas ;  and  even  with  these  small 
pieces,  pupils  should  be  warned  to  stand  back  when  dropping  them 
into  water. 

Among  the  sodium  salts  which  are  studied  in  this  chapter,  two 
are  especially  worthy  of  detailed  study  on  account  of  their  extensive 
use  in  daily  life.  These  are  the  bicarbonate  and  the  carbonate  of 
sodium.  Pupils  may  well  be  allowed  to  prepare  them  individually 
in  the  laboratory.  The  bicarbonate  may  readily  be  made  by  a 
method  very  similar  to  the  Solvay  process  as  described,  but  not  in 
detail,  in  Section  190,  p.  180. 

The  carbonate  can  then  be  made  from  the  bicarbonate  by  heating 
the  latter.  The  last  experiment  may  be  conducted  as  a  quantita- 
tive experiment  if  desired.  The  first,  if  made  quantitatively,  illus- 
trates the  difference  between  theoretical  yield  and  actual  yield 
in  chemical  processes  for,  owing  to  the  relatively  great  solubility 
of  the  sodium  bicarbonate,  its  precipitation  is  incomplete. 

If  it  is  thought  desirable,  pupils  can  make  baking  powder  from 
sodium  bicarbonate  together  with  cream  of  tartar,  or  some  other 
suitable  dry,  solid  acid. 

The  enormous  use  of  sodium  carbonate  in  the  arts  and  as  a  water 
softener  and  cleanser  should  be  discussed  in  the  classroom. 

The  easily  efflorescent  character  of  the  deca-hydrate  of  sodium 
carbonate  affords  an  opportunity  to  study  the  subject  of  crystal 
hydrates,  and  this  study  may  be  made  quantitative  if  time 
permits. 

Sodium  hydroxide  may  be  made  by  the  reaction  of  sodium  car- 
bonate and  slaked  lime,  thereby  bringing  another  commercial  re- 
action of  great  importance  to  the  attention  of  the  pupils. 

The  uses  of  the  sodium  hydroxide  should  then  be  studied,  es- 
pecially its  use  in  soap  making.  The  study  of  sodium  nitrate  and 
of  potassium  salts  in  this  chapter  may  be  enlarged  upon,  in  con- 
nection with  their  use  in  fertilizers.  This  is  especially  desirable  in 


60  SODIUM 

rural  communities,  where  the  information  may  later  be  of  practical 
value  to  some  of  the  pupils. 

Glass  making  should  be  discussed  in  class,  while  considering 
sodium  and  potassium  compounds,  and  the  broader  fundamentals 
of  its  chemistry  taken  up.  As  glasses  are  usually  very  complex 
mixtures  of  the  silicates  of  various  metals,  no  very  complete  chemi- 
cal treatment  can  be  made  with  elementary  chemistry  students. 

Answers  to  Questions  on  Chapter  XVII 
Page  191 

1.  Common  salt  is  the  chief  source  of  sodium  compounds,  not 
only  on  account  of  its  abundance  but  also  because  it  contains  a  high 
per  cent  of  sodium,  and,  being  soluble,  it  is  easily  purified.     Other 
abundant   materials   containing   sodium,    such   as   soda  feldspar, 
Na20  •  A1203  •  6  Si02,  mica,  Na20  •  3  A1203  •  6  Si02  •  2  H20,  and  cry- 
olite, A1F3 .  3  NaF,  are  insoluble  in  water  and  require  rather  elabo- 
rate chemical  treatment  for  their  decomposition. 

2.  See  Section  192,  p.  183,  and  last  paragraph  of  Section  60, 
p.  61. 

3.  See  Section  193,  p.  184. 

4.  See  Section  193,  p.  184. 
6.   See  Section  195,  p.  185. 

6.  Metallic  sodium  is  protected  from  the  action  of  the  air  by 
being  immersed  in  kerosene,  or  a  similar  oil,  which  contains  no  com- 
bined oxygen  and  dissolves  very  little  oxygen  or  water  vapor  from 
the  air. 

7.  A  bit  of  sodium  exposed  to  the  air  becomes  first  covered  with 
a  dull  film ;  this  soon  becomes  white  and  grows  moist  and  little  bub- 
bles are  seen  to  puff  it  up.     Gradually  the  surface  grows  more  and 
more  liquid  and  the  lump  seems  to  melt  into  a  little  puddle  of  rather 
viscous  liquid  with  some  solid  white  residue  in  the  bottom.     Finally 
the  liquid  dries  up  and  a  caked  mass  of  white  solid  remains. 

First  the  metal  reacts  with  the  moisture  of  the  air  (which  is  far 
more  abundant  than  carbon  dioxide) 

2  Na  +  2  H20  -+  2  NaOH  +  H2 
The  NaOH  forms  the  white  crust  and  the  hydrogen  gives  rise  to  the 


PAGES  177-191  61 

bubbles.  The  NaOH  absorbs  more  water  and  dissolves  in  it,  thus 
accounting  for  the  wet  surface  and  the  viscous  solution.  The  C02 
of  the  air  reacts  with  the  NaOH. 

2  NaOH  +  C02  ->  Na2C03  +  H20 

The  Na2CO3  is  the  white  solid  which  separates  from  the  NaOH  solu- 
tion in  which  it  is  not  very  soluble.  Finally,  since  Na2C03  does 
not  have  the  attraction  for  water  possessed  by  NaOH,  the  liquid 
evaporates  and  leaves  dry  sodium  carbonate  (see  Section  195, 
p.  185). 

8.  The  substance  is  sodium  chloride. 

9.  Sodium  hydroxide  might  be  used  to  dry  gases  on  account  of  its 
attraction  for  water  vapor  (see  Section  195,  p.  185). 

10.  See  Section  192,  p.  183. 

11.  Sodium  bicarbonate  is  preferred  to  sodium  carbonate  in  fire 
extinguishers  because,  for  the  same  amount  of  sodium,  it  yields  twice 
as  much  carbon  dioxide,  and  for  the  same  yield  of  carbon  dioxide 
only  one  half  as  much  acid  is  required  ; 

2  NaHCOs  +  H2S04  ->  Na2S04  +  H20  +  2  C02 
Na2C03  +  H2S04  ->  Na2S04  +  H20  +  C02 

12.  3  Na    +  A1C13  ->  3  NaCl  +  Al 
3  X  23  27.1 

Let  x  =  weight  of  Al  obtained. 
Then  69:  27.1::  1000  :x. 
x  =  392  g.  of  Al 

13.  Na2C03  +  CaC03  +  6  Si02  ->  Na20  -  CaO  •  6  Si02  +  2  C02 

106  100.1         361.8  479.9 

479.9  :  106     : :  1000  :x          x  =  220.9  kg.  of  Na2C03  | 
479.9  :  100.1 : :  1000 :  x  x  =  208.5  kg.  of  CaC03  |  Answer 

479.9  :  361.8  : :  1000  :x  x  =  754.5  kg.  Si02 

14.  According  to  the  equation,  for  each  gram  formula  weight 
of  glass  produced,  2  moles  of  C02  gas  escape  =  2  x  22.4  =  44.8 
liters. 

Since  1000  liters  =  1  cubic  meter,  for  each  kilogram  formula 
weight  of  glass  there  will  be  44.8  cu.m.  of  C02  measured  under  stand- 
ard conditions. 

Then  479.9  :  44.8  : :  1000  :  x, 
and  x  =  93.34  cubic  meters  C02  under  standard  conditions. 


62  CALCIUM 

CHAPTER   XVIII 

CALCIUM 

Pages  192-206 

METALLIC  calcium  is  deserving  of  wider  use  in  the  laboratory  now 
that  it  is  comparatively  cheap.  It  is  far  safer  for  pupils  to  use  than 
sodium  or  potassium,  and  being  active  enough  to  decompose  water 
in  the  cold,  it  serves  admirably  to  illustrate  the  properties  of  a  very 
active  metal. 

The  use  of  calcium  chloride  as  a  drying  agent  and  the  general 
topic  of  deliquescence  will  naturally  be  enlarged  upon  in  class  in 
connection  with  the  study  of  the  calcium  compounds. 

The  use  of  concentrated  sulphuric  acid  and  of  phosphorus  pen- 
toxide  as  still  more  efficient  drying  agents  for  gases,  may  be  men- 
tioned here. 

The  lime  industry  is  so  important  practically  that  the  chemistry 
of  limestone,  lime,  and  slaked  lime  should  be  given  considerable 
attention. 

The  chemistry  of  the  setting  of  mortar  and  plaster  should  then 
be  taken  up.  Avoid  giving  the  too  common  belief  that  the  carbon 
dioxide  reaction  with  the  lime  in  the  mortar  is  either  prompt  or 
complete,  for  it  is  said  that  considerable  calcium  hydroxide  remains 
in  the  mortar  for  a  long  time.  The  drying  out  of  the  mortar  is 
probably  largely  responsible  for  much  of  the  first  stiffness. 

The  chemistry  of  calcium  bicarbonate  is  vastly  interesting  be- 
cause of  its  connection  with  the  temporary  hardness  of  water  and 
with  cave  formation.  The  chemistry  of  magnesium  bicarbonate  and 
ferrous  bicarbonate  is  so  similar,  and  all  three  bicarbonates  are 
so  likely  to  be  present  in  hard  waters,  that  they  may  be  mentioned 
at  this  time. 

Calcium  sulphate  is  briefly  treated  before  going  into  the  dis- 
cussion of  hard  water  because  it  is  mainly  responsible  for  perma- 
nent hardness. 

Plaster  of  Paris  is  sufficiently  important  practically  to  deserve 
passing  mention.  The  preparation  and  setting  of  this  substance 


PAGES  192-206  63 

can  be  explained  by  recalling  what  was  learned  about  crystal  hy- 
drates (see  Section  194,  p.  185). 

As  the  setting  of  cement  depends  largely  on  hydration  of  certain 
silicates,  and  as  the  concrete  industry  is  of  such  vast  importance, 
it  may  be  worth  while  to  digress  at  this  point  sufficiently  to  consider 
the  general  principles  involved.  Some  cement  can  be  secured  and 
the  classes  can  then  construct  a  simple  mold  and  secure  gravel  or 
crushed  stone  and  make  up  some  object,  perhaps  something  that  will 
be  useful  about  the  building.  The  practical  side  of  this  subject 
deserves  more  attention  in  rural  schools  than  in  city  schools. 
Teachers  will  use  their  own  judgment  as  to  the  amount  of  time  they 
can  afford  to  spend  on  such  applications  of  chemistry  to  the  affairs 
of  daily  life. 

Similarly,  the  amount  of  time  to  be  spent  in  considering  water 
softening  and  in  experimenting  with  various  water  softeners,  should 
depend  upon  the  extent  of  the  community  interest  in  the  subject. 
It  is  of  little  practical  importance  where  pure  soft  water  is  used  and 
of  vast  importance  to  the  industries  and  to  the  home  in  those  sec- 
tions of  the  country  which  are  afflicted  with  hard  water.  In  schools 
in  places  of  the  latter  type,  considerable  interest  will  be  found 
in  testing  some  of  the  preparations  sold  under  fanciful  names  as 
water  softeners.  Tests  for  sodium  carbonate,  tri-sodium  phosphate, 
borax,  sodium  fluoride,  or  sodium  aluminate  may  be  made,  as  some 
one  (or  more)  of  these  substances  is  usually  present.  The  use  of 
ammonia  water  in  household  water  softening  and  the  use  of  soap  for 
the  purpose  should  of  course  be  explained.  A  visit  to  a  laundry 
which  softens  the  water  used  in  washing  clothes  will  be  interesting 
and  profitable. 

Having  now  studied  oxygen,  a  bivalent  non-metallic  element, 
chlorine,  which  is  monovalent  toward  hydrogen,  and  sodium  and 
calcium,  metals  which  are  respectively  mono-  and  divalent,  a  few 
paragraphs  on  the  subject  of  valence  can  be  introduced  at  this 
point  with  profit.  The  use  of  the  idea  in 'future  chapters  will 
gradually  develop  it,  until  in  Chapter  XXVII  a  much  more  complete 
discussion  of  the  subject  can  be  given  after  the  hydrogen  equiva- 
lents of  sodium  (monovalent),  magnesium  (divalent),  and  alu- 
minium (trivalent)  have  been  determined. 


64  CALCIUM 

Answers  to  Questions  on  Chapter  XVIII 
Page  205 

1.  Metallic  calcium  is  a  very  active  substance,  reacting  at  ordi- 
nary temperature  with  water  and  at  elevated  temperature  com- 
bining vigorously  with  oxygen  and  even  with  nitrogen.     Hence  it 
is  never  found  as  free  metal  in  nature. 

2.  See  Sections  207  and  208,  pp.  195  and  196. 

3.  See  Sections  207,  208,  209,  pp.  195-199. 

4.  See  Section  209,  p.  197. 
6.   See  Section  211,  p.  199. 

6.  Stalactites  are  icicle-like  formations  which  hang   from  the 
roofs  of  caves.     When  carbonated  water  which  on  flowing  through 
limestone  beds  has  dissolved  calcium  carbonate  hangs  in  drops  from, 
the  roof  of  the  cave  or  trickles  down  the  surface  of  the  stalactites, 
some  of  the  carbon  dioxide  escapes  from  the  solution  into  the  air 
of  the  cave.     Thus  the  solvent  power  for  calcium  carbonate  is 
diminished  and  some  of  this  substance  is  deposited.     If  there  is  a 
constant  trickle  of  the  water  and  if  the  air  is  moving  so  as  to  carry 
away  the  carbon  dioxide,  large  stalactites  are  gradually  formed. 

7.  In  the  household,  hard  water  can  be  softened  by  adding  am- 
monia or  sodium  carbonate.     Ammonia  neutralizes  the  excess  of 
carbonic  acid  in  a  temporary  hard  water, 

H2C03  +  2  NH4OH  -+  (NH4)2C03  +  2  H2O, 
and  with  the  removal  of  carbonic  acid,  calcium  carbonate  precipi- 
tates.    If  the  hardness  is  of  the  permanent  variety,  sodium  carbon- 
ate will  precipitate  calcium  or  magnesium  salts, 

CaCl2  +  Na2C03  ->  CaC03 1  +  2  NaCl 
Ca(HC03)2  +  Na2C03  ->  CaCO  d  +  2  NaHC03 
It  is  to  be  noted  from  the  last  equation  that  temporary,  as  well 
as  permanent,  hardness  is  removed  by  the  use  of  sodium  carbonate. 

8.  In  dry  air  only  a  thin  superficial  film  of  oxide  or  hydroxide 
forms  over  metallic  calcium,  and  this  excludes  oxygen  fairly  well 
from  the  underlying  layers.     Hence  the  most  satisfactory  way  to 
keep  calcium  is  in  dry  stoppered  bottles.     The  advantage  of  more 
completely  excluding  oxygen  by  using  kerosene  does  not  compensate 
for  the  inconvenience. 


PAGES  192-206  65 

Sodium  and  potassium  can  likewise  be  kept  in  dry  tight  bottles 
which  are  infrequently  opened,  but  the  surface  films  of  oxide  or 
hydroxide  have  so  great  an  attraction  for  water,  that  it  is  more 
difficult  to  keep  them  in  this  way. 

9.  Sea  water  may  be  softened  for  use  in  the  boilers  of  a  battle- 
ship by  the  addition  of  sodium  carbonate,  which  removes  the 
troublesome  calcium  and  magnesium  salts.     But  as  the  water  is 
converted  to  steam  much  sodium  salt  is  left  and  even  this  will  soon 
begin  to  separate  as  a  solid  in  spite  of  its  considerable  solubility,  un- 
less the  boilers  are  frequently  "  blown  off." 

Distillation  may  also  be  resorted  to,  and  of  course  this  method 
would  also  furnish  water  fit  for  drinking. 

10.  See  Section  206,  p.  194. 

11.  See  Section  212,  p.  201. 

12.  CaO  +  H20  ->  Ca(OH)2 
56.1        18 

56.1:  18::  1000:  a: 
x  =  320.9  grams  H20. 

13.  CaO  +  H20  ->  Ca(OH)2 
Ca(OH)2  +  CO2  ->  CaC03  +  H2O 

adding,    "  CaO    +  CO2  ->  CaCO3 

56.1  g.     22.4  1.     100.1  g. 
56.1:22.4::  1000 :  x 

x  =  399.3  liters  CO2  under  standard  conditions. 
56.1:100.1::  1000  :x 
x  =  1784  grams  air-slaked  lime. 
14. .  1  liter  contains  0.5  g.  CaS04 
1000  liters  contain  500  g.  CaS04 

CaS04  +  Na2C03  -^  CaC03  +  Na2SO4 
136.2          106 
136.2  :  106 : :  500  :  x 
x  =  389.8  grams  Na2C03. 

15.  2  NaC18  H35  02  +  CaS04  ->•  Ca(Ci8  H35  02)2  +  Na2S04 

612  136.2 

612  :  136.2  : :  x  :  0.5 
x  =  2.25  grams  of  soap. 

16.  The  pupil  is  expected  in  this  question  to  consult  the  atomic 


66  ACIDS  AND  BASES;    NEUTRALIZATION 

weight  table  in  order  to  be  able  to  name  the  hitherto  unfamiliar 
elements  whose  symbols  are  given.  It  is  to  be  taken  for  granted 
that  in  such  compounds,  as  for  example  Mn207  all  of  the  valences 
of  the  non-metal  are  held  by  the  valences  of  the  metallic  element. 
Thus  the  two  atoms  of  manganese  must  be  exerting  14  metallic 
valences  to  hold  the  7  X  2  =  14  non-metallic  valences  of  the  7 
oxygen  atoms,  and  each  atom  of  Mn  is  therefore  exerting  7  valences. 
In  other  words,  the  valence  of  Mn  is  7.  The  pupil  should  note  that 
the  valence  of  an  element  may  be  different  in  different  compounds 
as  that  of  tin  in  SnCl2  and  SnCl4. 

It  should  be  emphasized  that  the  kind  of  attraction  exerted  by 
metals  is  fundamentally  opposite  in  character  from  that  exerted  by 
non-metals.  One  is  called  positive  and  the  other  negative.  It 
may  not  be  too  soon  to  suggest  the  probable  electrical  nature  of 
valence. 

CHAPTER   XIX 

ACIDS   AND   BASES;    NEUTRALIZATION 

Pages  207-219 

SINCE  the  majority  of  inorganic  substances  can  be  classed  either 
as  acids  or  bases,  or  as  salts,  which  are  a  product  of  the  neutral- 
ization of  acids  and  bases,  it  follows  that  a  somewhat  complete 
study  of  the  fundamentals  of  the  chemistry  of  these  substances  is 
necessary. 

After  recalling  the  fact  that  hydrogen,  in  a  peculiar  state  of  com- 
bination, is  a  characteristic  component  of  all  acids  (see  Section  111, 
p.  1 12 ,  for  a  previous  hint  of  this  matter)  the  design  of  the  chapter  is  to 
show,  first  that  the  non-metallic  elements  are  essentially  acid  formers 
and  that  by  oxidizing  them  and  allowing  the  oxides  to  react  with 
water,  acids  are  produced.  Several  examples  of  this  sort  of  behavior 
are  given  before  it  is  announced  that  this  type  of  reaction  is  general 
to  the  non-metals. 

It  should  be  clearly  pointed  out  that  it  is  the  hydrogen  of  the 
water  that,  under  the  influence  of  the  non-metallic  oxide,  becomes 
the  hydrogen  of  the  acid. 


PAGES  207-219  67 

After  the  nature  of  the  formation  of  acids  has  been  pointed  out,  a 
similar  treatment  of  the  bases  follows,  in  which  their  metallic  origin 
is -shown.  Here  the  presence  of  the  OH  group  as  the  characteristic 
group  of  all  bases  should  be  emphasized. 

The  treatment  of  neutralization  as  a  union  of  the  characteristic 
hydrogen  of  an  acid  with  the  hydroxyl  of  a  base  to  form  water  is 
then  easy.  That  the  other  components  of  the  acid  and  base  yield 
a  salt  solution,  which  on  evaporation  of  the  water  gives  a  salt, 
should  be  taught  as  an  auxiliary  reaction  rather  than  as  the  prin- 
cipal reaction  in  neutralization. 

Answers  to  Questions  on  Chapter  XIX 

Page  218 

1.  The  sour  taste  of  cream  of  tartar  resembles  the  sour  taste 
common  to  all  acids,  and  it  shows  that  cream  of  tartar  must  contain 
acid  hydrogen. 

2.  The   alkaline  taste  shows  the  presence  of   basic  hydroxyl 
groups. 

3.  Chemically  water  is  composed  of  the  elements  which  would 
constitute  the  acid  hydrogen  and  the  basic  hydroxyl  group,  yet  water 
possesses  none  of  the  characteristic  properties  such  as  taste,  or  ef- 
fect on  litmus,  of  either  of  these  components.     Hence,  it  is  obvious 
that  in  water  these  two  components  are  so  bound  to  each  other  that 
they  are  unable  to  show  their  usual  properties.     When  acid  and  base 
are  brought  together,  then,  it  is  very  natural  that  these  components 
should  at  once  form  water  and  thus  disappear  as  distinct  compo- 
nents. 

4.  See  Sections  230,  231,  p.  215. 

6.  Sodium  sulphate  may  be  made :  (a)  from  sodium  hydroxide  by 
neutralizing  it  with  sulphuric  acid, 

2  NaOH  +  H2S04  ->  Na2S04  +  2  H20 

(6)  from  sodium  chloride  by  adding  sulphuric  acid  and  heating 
to  drive  off  the  volatile  hydrochloric  acid  (Section  139,  p.  134), 

2  NaCl  +  H2S04  ->  Na2S04  +  2  HC1  * 

(c)  from  sodium  carbonate  by  adding  sulphuric  acid,  thus  bring- 
ing together  the  components  of  the  weak  and  unstable  acid  H2CO3. 


68        .  ACIDS  AND  BASES;    NEUTRALIZATION 

This  acid  decomposes  with  the  escape  of  C02,  and  sodium  sulphate  is 
left, 

Na2C03  +  H2S04  ->  Na2S04  +  H2C03 


6.  Ammonia  water  contains  the  weak  and  non-corrosive  base 
NH4OH.     It  is  used  rather  than  sodium  hydroxide  to  prevent  sul- 
phuric acid  eating  holes  in  clothes  because  it  is  itself  harmless,  and 
yet  it  neutralizes  the  corrosive  acid  as  effectively  as  does  the  even 
more  corrosive  base.     Furthermore,  all  excess  of  ammonia  not  used 
in  the  neutralization  is  volatile  and  evaporates  from  the  clothes. 

7.  If  "  sour  "  stomach  is  caused  by  too  much  acid  it  is  obvious 
that  lime  water  containing  the  base  Ca(OH)2  will  neutralize  the 
acid. 

8.  The  40  grams  of  NaOH  =  1  mole.     From  the  equations  : 

NaOH  +  HC1  ->  NaCl  +  H2O 
2  NaOH  +  H2S04  ->  Na2S04  +  2  H20 

it  is  obvious  that  1  mole  of  HC1  or  36.5  grams,  and  £  mole  of  H2S04 
or  49  grams  are  necessary  to  neutralize  one  mole  of  base. 

9.  2  NaOH  +    C02  ->  Na2C03  +  H20 

80  g.          22.4  1. 

It  is  obvious  that  40  grams  of  NaOH  will  require  \  X  22.4  =  11.2 
liters. 

10.  2  NH3  +  H2S04  ->  (NH4)2S04 
44.8  1.       98  g. 

If  x  =  volume  of  ammonia  gas 
Then  98  :  44.8  :  :  1000  :  x 

x  =  457  liters  of  ammonia  gas. 

11.  If  1  liter  of  the  solution  contains  200  g.  of  HC1,  100  c.c.  of 
the  solution  will  contain  20  g.  of  HC1. 

HC1  +  KOH  -*  KC1  +  H20 
36.5        56.1 
Let  x  =  weight  of  KOH  required 

36.5  :  56.1  :  :  20  :  x  x  =  30.74  g.  of  KOH. 

Since  1  liter  of  the  KOH  solution  contains  100  g.  of  KOH,  the  volume 

which  will  contain  30.74  grams  =  ^i  x  1000  =  307.4  c.c. 

101) 

12.  See  Sections  222,  223,  224,  226,  227,  pp.  210-214. 


PAGES  220-224  69 

CHAPTER  XX 

NOMENCLATURE 
Pages  220-224 

THIS  brief  chapter  on  nomenclature  is  naturally  called  for  im- 
mediately after  the  discussion  of  acids,  bases,  and  salts,  as  many 
opportunities  for  practice  in  the  use  of  chemical  names  arise  out 
of  the  latter  subject.  Future  progress  in  the  study  of  chemistry 
depends  to  some  degree  upon  facility  in  the  correct  use  of  the  names 
of  chemical  substances. 

In  this  work,  methods  such  as  are  successful  in  the  study  of 
language  should  be  used,  and  pupils  will  be  found  to  have  little  diffi- 
culty with  the  subject,  if  given  sufficient  opportunity  to  practice  it. 
After  the  first  formal  instruction  from  the  textbook  is  over,  much 
help  will  be  had  from  a  rapid  drill  upon  the  names  of  all  the  acids, 
bases,  and  salts  present  in  the  laboratory  or  classroom.  The 
teacher  can  furnish  in  turn  the  names  of  the  substances  and  require 
from  the  pupils  the  names  of  the  related  acid,  base,  or  salt  as  the  case 
may  be.  For  example,  if  sodium  nitrate  be  at  hand,  the  teacher  may 
ask,  "  From  what  acid  may  sodium  nitrate  be  made?  With  what 
base?  "  Or,  again,  "  This  is  a  salt  made  by  the  union  of  sodium 
hydroxide  with  nitric  acid.  What  is  its  name?  "  etc.  Or,  if  a  me- 
tallic oxide  be  at  hand,  "  This  is  iron  oxide.  What  should  the  prod- 
uct of  its  reaction  with  water  be  called?  "  etc.  After  sufficient 
drill  with  the  names  of  familiar  substances,  the  teacher  may  intro- 
duce names  that  are  unfamiliar  to  the  pupils  in  order  to  see  if  the 
pupils  have  really  learned  the  scheme  for  the  changes  in  endings  of 
the  names,  or  if  they  have  merely  memorized  the  particular  names 
that  have  been  employed.  Citric  acid  and  the  citrates,  tartaric 
acid  and  the  tartrates,  hypophosphorous  acid  and  the  hypophos- 
phites,  permanganic  acid  and  the  permanganates,  etc.,  may  be  used. 

Answers  to  Questions  on  Chapter  XX 

Page  224 
All  answers  are  obvious  from  the  rules  given  in  the  textbook. 


70  THE  METALS 

CHAPTER  XXI 

THE    METALS 

Pages  225-238 

THE  pupil  already  possesses  at  this  point  in  his  study  some  frag- 
mentary knowledge  of  the  metals,  for  he  has  had  to  consider  the 
metals  in  studying  the  way  in  which  they  form  compounds  with 
the  non-metals.  Instead  of  postponing  a  systematic  study  of  the 
metals  until  a  second  part  of  the  book  and  then  giving  a  rather  dry 
recital  of  the  properties  of  the  salts  of  each  metal  in  turn,  it  is 
deemed  better  to  give  at  this  point  a  somewhat  careful  study  of 
the  main  characteristics  of  the  metals,  and  the  differences  among 
the  broader  groups  of  metals.  This  chapter  leads  up  to  the  follow- 
ing chapter  on  metallurgy,  which  considers  the  occurrence,  separa- 
tion from  ores,  and  main  uses  of  the  more  important  metals.  The 
next  chapter  thus  illustrates  and  fixes  more  firmly  in  the  mind  some 
of  the  general  principles  brought  out  in  this  chapter.  Nowhere  in 
the  book  is  an  enumeration  of  the  properties  of  the  salts  of  each 
metal  in  turn  undertaken.  The  pupil  should  learn  to  rely  on  his 
knowledge  of  the  metal  to  know  the  character  of  the  base  that  can 
be  formed  from  it,  and  to  rely  on  his  knowledge  of  the  acid  and 
base  and  of  salts  in  general  to  know  approximately  what  a  particular 
salt  is  like.  Appendixes  VI  and  VII  on  page  430  will  be  useful  in 
finding  the  solubilities  of  salts,  and  whenever  occasion  arises  to 
need  exact  information  regarding  a  salt,  reference  should  be  made 
to  a  handbook,  after  first  defining  the  general  character  of  the  salt 
from  a  consideration  of  the  acid  and  the  base. 

The  electrical  nature  of  the  difference  between  metals  and  non- 
metals  is  here  first  suggested,  and  although  this  point  may  very 
well  be  kept  in  the  background,  it  may,  if  followed  up,  lead  to  in- 
teresting deductions.  If  the  electrical  side  of  combination  is  to 
be  considered  at  all,  it  should  be  emphasized  that  uncombined  ele- 
ments are  electrically  neutral ;  it"  is  only  when  they  enter  into  the 
combined  state  that  they  acquire  charges,  the  metals  positive 
charges,  the  non-metals  negative  charges.  On  separating  from  the 


PAGES  225-238  71 

state  of  combination  elements  part  with  whatever  free  electrical 
charges  they  possessed.  Failure  to  appreciate  this  point  accounts 
for  the  failure  of  the  earlier  chemists  to  develop  a  satisfactory  elec- 
trochemical theory.  Since,  however,  the  electrification  of  constitu- 
ents of  compounds,  with  the  exception  of  acids,  bases,  and  salts,  is  so 
well  concealed  that  all  chemists  do  not  even  admit  its  existence, 
it  is  not  particularly  recommended  that  the  teacher  go  far  in  this 
line  of  argument,  for  the  enthusiastic  pupils  are  sure  to  carry  the 
idea  beyond  where  the  teacher  would  willingly  stop. 

In  this  chapter  the  metals  are  divided  into  three  general  classes, 
the  alkali  metals,  the.  earth-forming  metals,  and  the  heavy  metals. 
The  great  chemical  activity  of  the  metals  of  the  first  two  classes 
is  brought  out  and  the  lack  of  practical  usefulness  because  of  this 
property  should  be  emphasized  by  the  teacher.  Aluminium  is 
the  only  metal  of  those  in  the  first  two  groups  that  is  largely  in 
practical  use,  and  its  usefulness  is  possible,  in  spite  of  its  great 
activity,  because  it  acquires  a  protective  coating  of  its  own  oxide. 
The  preparation  of  aluminium  illustrates  again  its  great  reactivity, 
requiring  the  use  of  electrolysis  rather  than  the  simple  methods 
of  reduction  in  use  with  the  heavy  metals.  The  similar  preparation 
of  sodium  has  already  been  discussed  (Section  186,  p.  177).  The 
use  of  aluminium  in  aluminothermy  (Section  434,  p.  415)  may  be 
referred  to  here  as  further  evidence  of  the  great  chemical  activity  of 
this  member  of  the  earth-forming  metals. 

Leaving  the  more  active  metals,  we  come  to  the  more  familiar 
metals  of  the  group  which  we  have  called  the  heavy  metals.  Be- 
fore entering  upon  a  detailed  study  of  the  means  of  recovering  these 
metals  from  their  ores,  a  brief  study  of  their  relative  degree  of  activ- 
ity is  made.  This  in  reality  anticipates  their  positions  in  the  elec- 
tromotive series  (Section  347,  p.  329)  and  should  be  made  by  the 
teacher  to  hark  back  to  the  displacement  of  hydrogen  by  zinc,  iron, 
etc.,  but  not  by  copper,  silver,  gold,  etc. 

This  study  of  relative  activity  gives  the  underlying  explanation  as 
to  why  some  of  the  metals  of  this  group  are  found  free  in  the  earth, 
while  the  others  are  found  in  combination  with  non-metals  and  re- 
quire the  various  treatments  that  are  to  be  described  in  the  follow- 
ing chapter  on  metallurgy. 


72  THE  METALS. 

Answers  to   Questions  on  Chapter  XXI 
Page  238 

1.  See  Sections  241,  242,  pp.  225,  226. 

2.  See  Section  243,  p.  227. 

3.  See  Section  246,  p.  229. 

4.  See  Section  245,  p.  229. 

5.  See  Section  247,  p.  230. 

6.  See  Section  248,  p.  230. 

7.  See  Section  249,  p.  232. 

8.  See  Section  250,  p.  232. 

9.  Find  the  specific  gravity  of  the  metals  in  Appendix,  p.  427. 

10.  See  Section  253,  p.  237. 

11.  See  Section  251,  p.  234. 

12.  Silver,  platinum,  and  gold  are  the  metals  which  can  best 
be  used  for  jewelry. 

13.  When  zinc  is  exposed  to  the  weather,  its  surface  is  quickly 
oxidized  and  a  film  consisting  probably  of  hydroxide  is  formed  on 
the  surface.     This  film  adheres  firmly,  and  moreover  is  close  in 
texture  so  that  air  and  water  are  excluded  from  the  metal  beneath. 
On  the  other  hand,  the  film  of  iron  hydroxide  formed  by  the  action 
of  the  weather  on  iron  is  scaly  and  porous  and  does  not  exclude 
the  weather.     Hence,  in  spite  of  its  greater  activity,  zinc  is  superior 
to  iron  for  use  on  roofs. 

14.  The  table  on  page  235  shows  that  tin  is  a  less  active  metal 
than  iron.     Hence  tin  would  be  less  quickly  attacked  by  the  acids 
present  in  food  products.    Furthermore,  molten  tin  adheres  well  to  a 
clean  iron  surface  so  that  it  is  very  easy  to  obtain  a  tinned  surface 
on  sheet  iron. 

Tin  is  not  a  perfect  metal  for  the  purpose,  because  as  seen  from 
the  table,  tin  is  more  active  than  hydrogen.  It  does  displace  hy- 
drogen slowly  from  hydrochloric  acid,  thus  forming  soluble  tin 
chloride.  It  would  also  be  able  to  displace  hydrogen  from  the  weak 
acids  in  canned  goods,  although  of  course  more  slowly,  because  the 
acids  are  weaker.  Thus  tin  salts  might  get  into  the  food.  Tin 
salts  in  small  amounts  are  not  dangerously  poisonous,  although  they 
are  not  desirable  in  food. 


PAGES  239-263  73 

15.  Structural  iron  is  preserved  from  corrosion  by  painting  or  by 
surrounding  with  cement.  Note :  Cement  is  not  impervious  to  air 
or  water,  but  cement  always  contains  sufficient  calcium  hydroxide 
to  give  a  slight  degree  of  alkalinity.  This  would  neutralize  any 
possible  acid  (as  from  smoke)  which  might  get  at  the  iron.  Acidity 
is  one  of  the  most  powerful  factors  in  promoting  the  rusting  of  iron. 


CHAPTER  XXII 

METALLURGY 

Pages  239-263 

IN  this  very  practical  chapter  the  metallurgy  of  the  commonest 
metal,  iron,  is  first  taken  up  and  the  principles  as  well  as  the  prac- 
tice, dwelt  upon  quite  extensively.  The  related  subject,  the  nature 
and  preparation  of  steel,  is  also  given  much  space.  Because  of  its 
practical  importance,  steel  deserves  a  good  deal  of  attention. 
Wherever  possible,  pupils  should  be  given  an  opportunity  to  visit 
such  iron  or  steel  plants  as  the  vicinity  affords,  even  if  it  is  only  a  trip 
to  see  a  cupola  in  which  cast  iron  is  melted,  or  to  a  blacksmith's 
shop  to  see  the  heat  treatment  of  steel  in  hardening  and  tempering. 

In  connection  with  the  metallurgy  and  the  refining  of  copper,  a 
small  sample  of  powdered  copper  sulphide  ore  may  be  roasted  in  a 
porcelain  crucible  and  then  the  resulting  oxide  reduced  to  metallic 
copper  by  passing  hydrogen  over  the  heated  oxide,  which  may  be 
placed  in  a  hard  glass  tube.  If  current  is  available,  the  transfer  of 
copper  from  a  thick  anode  to  a  thin  cathode  of  copper  may  be  made 
to  illustrate  the  electrolytic  method  of  refining  the  crude  metal. 

Pupils  will  be  found  to  be  much  interested  in  the  recovery  of 
precious  metals  in  copper  and  lead  refining.  If  such  refineries  are 
within  visiting  distance,  a  trip  to  one,  with  a  visit  to  the  strong 
room  where  the  gold  and  silver  are  kept,  will  afford  a  never-to-be- 
forgotten  experience  to  the  pupils.. 

Under  the  treatment  of  the  recovery  of  gold,  a  description  of  the 
simple  separation  by  means  of  differences  in  gravity  in  placer  mining 
will  interest  pupils. 


74  METALLURGY 

A  recently  patented  improvement  upon  the  amalgamation  proc- 
ess l  will  also  furnish  a  chance  to  apply  a  little  physics  and  further 
interest  pupils  in  the  subject.  It  seems  that  gold  as  found  in  nature 
is  sometimes  coated  over  with  iron  oxide  or  other  protective  coating 
so  that  it  is  not  dissolved  by  the  mercury  used  to  recover  it  from 
the  concentrates.  If  1  or  2  per  cent  of  zinc  be  added  to  the  mer- 
cury and  a  little  sulphuric  acid  to  the  wash  water,  a  "  couple^  "  is 
set  up  between  the  zinc  and  the  gold,  and  hydrogen  is  released  from 
the  gold  surfaces,  thus  loosening  the  scale-like  coating  so  that  the 
gold  dissolves  in  the  mercury.  This  method  will  probably  make 
possible  the  working  of  vast  deposits  of  low  grade  black  sands  in 
California  which  were  impossible  of  profitable  working  before. 

The  method  of  preparation  of  aluminium  serves  to  illustrate  the 
general  method  now  in  use  for  obtaining  highly  active  metals  from 
their  ores.  The  general  properties  of  the  metal  may  be  illustrated 
by  reference  to  its  large  and  increasing  use  in  kitchen  utensils. 

A  little  thermit  may  be  fired  off  to  illustrate  the  great  activity 
of  aluminium.  Place  not  more  than  50  grams  of  the  thermit  in  a 
clay  crucible  and  partly  embed  the  latter  in  a  large  pan  of  sand. 
Make  a  depression  in  the  middle  of  the  thermit  and  place  in  it  a 
little  of  a  mixture  of  equal  parts  of  photographic  flashlight  powder 
and  powdered  magnesium.  Stick  a  piece  of  magnesium  ribbon 
into  this  fuse  powder  and,  when  all  is  ready  to  set  off  the  mixture, 
set  fire  with  the  burner  to  the  upper  end  of  the  magnesium  ribbon, 
and  quickly  retire.  Caution :  Stand  at  least  ten  feet  from  the  crucible 
and  protect  with  asbestos  any  woodwork  near  the  reaction. 

Answers  to  Questions  on  Chapter  XXII 
Page  262 

1.  Tin  stone  consists  of  tin  dioxide,  Sn02.     The  most  obvious 
method  to  obtain  the  metal  therefrom  is  to  heat  the  oxide  with 
carbon.     Since  such  a  method  suffices  to  reduce  the  oxides  of  zinc 
and  iron,  it  must  surely  reduce  the  oxide  of  a  metal  that  is  less  ac- 
tive than  either  zinc  or  iron. 

2.  The  oxide  of  any  metal  less  active  chemically  than  zinc  should 

1  By  Prof.  R.  H.  Lyons  of  Indiana  University. 


PAGES  239-263  75 

be  reducible  with  carbon.  This  would  include  iron,  nickel,  tin, 
lead,  and  copper,  and  of  course  mercury  and  the  precious  metals 
whose  oxides  can  be  decomposed  by  mere  heating.  On  the  other 
hand,  it  is  unlikely  that  carbon  will  have  any  greater  attraction  for 
oxygen  than  the  very  active  metals,  aluminium,  magnesium,  cal- 
cium, barium,  sodium,  and  potassium.  In  no  case  can  the  oxides 
of  one  of  these  latter  be  completely  reduced  to  free  metal  by  means 
of  the  action  of  carbon.  Carbides;  however,  can  be  obtained  by  in- 
tense heating  of  the  oxides  with  carbon,  for  example  A14C3,  CaC2, 
and  by  heating  NaOH  with  carbon,  Na2C03  and  a  part  of  the  sodium 
in  the  metallic  condition  can  be  obtained, 

6  NaOH  +  2  C  ->  2  Na2C03  +  3  H2  +  2  Na. 

3.  The  method  of  electrolyzing  a  melted  compound  of  the  metal 
is  always  available  as  a  means  of  obtaining  the  free  metal,  when  the 
oxide  cannot  be  reduced  with  carbon. 

4.  Mercuric  oxide  decomposes  into  mercury  and  oxygen  when 
heated. 

6.   See  Section  274,  p.  260. 

6.  See  Section  265,  p.  253. 

7.  Copper  metal  may  be  precipitated  from  copper  sulphate  solu- 
tion by  hanging  strips  of  iron  in  the  solution.     The  iron  is  the  more 
active  metal  and  displaces  the  copper, 

Fe  +  CuS04  ->  FeS04  +  Cu  |. 

8.  Fe203  contains  70.0  per  cent  of  Fe ;     Fe304,  72.4  per  cent ; 
FeC03,  48.2  per  cent ;   Fe203  •  3  H20,  52.3  per  cent. 

9.  (a)  2  Cu20     +  C  ->  4  Cu  +  CO2 

2  x  143.2       12 
286.4  :  12  : :  1000 :  x 

x  =41.9  kilos  of  carbon. 
(6)  2  CuO     +  C  ->  2  Cu  +  C02 

2  x  79.6        12 
159.2  :  12  : :  1000  :  x 

x  =  75.4  kilos  of  carbon. 

10.  ZnO  +  C  ->  Zn  +  CO 
81.4       12 

81.4:  12::  1000  :x 

x  =  147.4  kilos  of  carbon. 


76  COMPOUNDS  OF  CARBON 

CHAPTER  XXIII 

COMPOUNDS    OF    CARBON 

Pages  264-281 

THE  study  of  carbon  compounds  is  taken  up  in  two  sections  in  sepa- 
rate chapters.  The  division  is  made  between  what  is  called  inor- 
ganic and  organic  chemistry,  but  care  has  been  taken  to  point  out 
that  this  division  is  purely  one  of  convenience  and  that  there  is  no 
essential  difference  between  the  chemistry  of  the  laboratory  and 
manufactory  on  the  one  hand  and  that  of  the  living  organism  on  the 
other.  Teachers  should  further  emphasize  the  unity  of  all  chemis- 
try in  this  respect.  Trips  to  municipal  gas  plants  may  be  made  with 
profit  in  connection  with  the  study  of  this  chapter.  They  will  be 
found  to  be  very  valuable,  both  on  account  of  the  objective  reality 
which  they  give  to  the  subject  matter  and  on  account  of  the  civic 
instruction  which  acquaintance  with  the  workings  of  such  public 
service  corporations  may  afford.  If  the  plant  visited  is  not  up  to 
date  and  the  charges  on  the  community  are  high,  the  pupils  ought 
to  know  it.  In  Indianapolis,  Indiana,  a  modern  by-product  coke 
oven  plant  of  the  Solvay  type  permits  the  sale  of  gas  to  small  con- 
sumers at  55  cents  per  1000  cubic  feet  and  to  large  users  at  con- 
siderably less,  and  at  the  same  time  pays  generous  dividends  on  all 
the  stock  of  the  company. 

Wherever  possible,  trips  should  be  taken  to  factories  where  water 
gas  or  producer  gas  is  made  and  here  again  there  is  value  both  in 
the  subject  matter  itself  and  in  the  knowledge  of  the  conditions  under 
which  many  men  have  to  make  their  living.  Some  very  hot  places 
to  work  in  will  be  found  in  some  of  these  plants,  and  the  question 
of  the  hours  of  labor  required  in  such  places  is  of  public  interest. 
The  teacher  who  teaches  only  chemistry  will  not  teach  chemistry 
itself  so  well  as  he  who  teaches  it  in  all  its  relations  to  mankind  and 
his  welfare. 

Under  the  study  of  Welsbach  mantles,  the  actual  exhibition  of 
one  and  a  study  of  its  brightness  when  held  over  a  common  Bunsen 
flame  as  compared  with  the  brightness  of  other  solids  when  made 


PAGES  264-281  77 

equally  hot  in  the  same  flame  will  prove  instructive.  Pupils  will 
also  be  interested  in  the  radioactivity  of  the  thorium  oxide  of  the 
mantle,  and  some  who  are  interested  in  photography  might  be  en- 
couraged to  expose  overnight  a  photographic  plate,  inclosed  in  a 
plate  holder,  to  the  action  of  a  strip  of  broken  mantle.  If  bits  of 
metal  of  various  shapes  be  laid  between  the  mantle  and  the  plate 
holder,  their  shadows  will  appear  in  the  developed  plate.  Although 
they  are  aside  from  the  main  topic,  such  studies  arouse  consider- 
able interest  in  the  subject  on  the  part  of  pupils. 

The  study  of  carborundum  can  be  made  more  interesting  if 
samples  of  the  beautifully  crystallized  material,  as  it  comes  from 
the  furnaces,  are  shown  to  the  class.  The  exhibition  of  hones  or 
grinding  wheels  made  of  the  material  will  also  add  to  the  interest. 
In  connection  with  the  discussion  of  the  great  hardness  of  carbo- 
rundum, the  popular  notion  that  it  is  as  hard  as  diamond  should 
be  corrected.  It  is  really  very  much  less  hard.  The  slightest  pres- 
sure will  cause  diamond  to  scratch  carborundum  deeply,  while  no 
amount  of  pressure  can  cause  carborundum  to  attack  diamond. 
However,  carborundum  is  considerably  harder  than  any  precious 
stone  other  than  diamond,  and  rubies  and  sapphires  are  easily  cut 
by  means  of  it.  Pupils  who  are  interested  in  art-metal  work  may  be 
encouraged  to  use  an  ordinary  coarse  carborundum  hone  to  shape 
pretty  pebbles  or  rough  semi-precious  stones,  which  is  easily  done  by 
rubbing  them  on  the  thoroughly  wet  stone  until  the  desired  shape  is 
obtained.  They  may  then  be  smoothed  by  the  use  of  fine,  and  then 
finer,  carborundum  cloth,  and  polished  by  rubbing  on  a  smooth 
board  with  well  wet  German  tripoli.  If  the  stone  to  be  polished  is 
cemented  on  to  a  penholder  by  means  of  a  mixture  of  melted  sealing 
wax  and  thoroughly  dried  plaster  of  Paris,  the  work  can  be  more 
readily  done.  The  cement  should  be  melted  over  a  flame  when  used. 
Lapidaries,  of  course,  use  rapidly  rotating  wheels  of  carborundum 
or  metal  wheels  impregnated  with  powdered  carborundum  and  water 
or  oil. 


78  COMPOUNDS  OF   CARBON 

Answers  to    Questions   on   Chapter   XXIII 

Page  281 

1.  The  most  valuable  form  of  carbon  from  the  viewpoint  of  price 
is  diamond.  For  economic  reasons  its  price  is  high  because  of  its 
scarcity  and  its  remarkable  hardness,  which  gives  it  a  value  for  cer- 
tain instruments  not  possessed  by  any  other  substance.  Its  great 
hardness  adds  to  its  desirability  as  a  gem  stone,  and  added  to  this 
we  have  its  crystal  clearness  and  the  beautiful  play  of  colors  given  by 
a  well-cut  stone.  But  other  stones  possess  considerable  hardness, 
crystal  clearness  and  beautiful  play  of  colors,  and  we  are  obliged  to 
conclude  that  the  very  high  price  paid  for  gem  diamonds  is  fictitious 
value,  and  arises  in  large  part  from  the  human  desire  to  possess  the 
rare  and  expensive  for  the  reason  alone  of  the  rareness  and  expense. 
Coal  and  charcoal  are  the  most  useful  forms  of  carbon  because  they 
constitute  our  most  valuable  fuels.  In  the  true  sense,  coal  is  more 
valuable  than  diamond  because  the  latter  is  in  no  way  essential 
to  human  welfare.  Other  substances  of  considerable  hardness  could 
be  substituted  for  it  in  all  important  instruments.  But  if  we  were 
deprived  of  coal,  a  complete  revolution  in  our  industries  and  our 
household  arrangements  would  be  necessary  before  our  lif e  could  be 
adjusted  to  the  new  conditions.  Indeed,  it  seems  very  doubtful  if 
satisfactory  substitutes  could  be  found  for  carbon  in  all  of  its  varied 
uses  in  furnishing  heat  and  power  and  in  the  metallurgical  industries. 

2  and  3.   See  Section  278,  p.  266. 

4.   See  Section  279,  p.  268. 

6.   See  Section  278,  p.  266. 

6.  See  Sections  283,  286  and  287,  pp.  270,  275,  and  276.    Al- 
though the  explanation  of  flame  luminosity  given  in  the  textbook  is 
a  serviceable  one,  in  that  it  would  enable  an  intelligent  person  to 
find  the  cause  of  poor  illumination  and  proceed  to  improve  it,  never- 
theless this  explanation  is  not  thorough,  for  it  does  not  touch  a  num- 
ber of  considerations  which  affect  luminosity. 

7.  See  Section  283,  p.  270.     For  convenience  in  explaining  the 
operation  of  the  valves,  number  them  1  to  6  inclusive  in  going  along 
the  operating  platform.      Ability  to  thus  explain  the  use  of   the 
valves  is  a  test   of    the    understanding    of    the    statements    in 


PAGES  264-281  79 

the  textbook.  Beginning  at  the  left  of  Fig.  55,  p.  271,  the 
first  valve  controls  the  admission  of  steam  to  the  generator.  The 
second  valve,  which  is  just  to  the  right  of  the  generator,  con- 
trols the  air  blast  to  the  generator.  The  third  valve  (beside  the 
second)  controls  the  admission  of  air  to  the  carburetor  during  the 
passage  of  the  producer  gas,  which  is  formed  when  air  is  being 
blown  through  the  thick  bed  of  coals  in  the  generator.  The  com- 
bustion of  this  producer  gas  serves  to  help  heat  the  carburetor  and 
also  the  superheater.  The  fourth  valve  controls  the  admission  of  oil 
to  the  carburetor.  It  is  immediately  above  the  latter.  The  fifth 
valve  serves  to  control  the  admission  of  air  to  the  superheater,  just 
as  the  third  serves  in  the  case  of  the  carburetor.  It  is  just  to  the 
right  of  the  carburetor.  The  sixth  valve  is  just  to  the  right  of  the 
smoke  stack.  When  closed  (during  the  active  combustion  period) 
no  gases  can  pass  into  the  scrubber.  When  the  stack  is  closed 
(during  the  admission  of  steam)  this  valve  is  opened  so  that  the 
water  gas  may  pass.  Note  that  during  the  combustion  period 
carbon  monoxide  (practically  producer  gas,  see  Section  284,  p.  271) 
is  produced  in  the  generator  and  that  it  is  the  combustion  of  this 
producer  gas  in  the  carburetor  and  the  superheater  which  serves  to 
heat  'these  to  the  required  degree. 

8.  See  Section  284,  p.  271.     The  economizer  serves  to  transfer 
the  heat  of  the  gases  coming  from  the  generator  to  the  air  entering 
the  generator.     The  diagram  represents  only  one  of  a  great  many 
modifications  of  gas  producers.     Often  the  economizer  is  not  used 
at  all,  and  the  down  draft  arrangement  of  the  generator  is  no  more 
frequent  than  the  up  draft. 

9.  See  Section  285,  p.  273. 

10.  Water  gas  will  give  a  hotter  flame  than  producer  gas,  for  the 
former  contains  practically  nothing  but  fuel,  whereas  the  latter 
contains  much  nitrogen,  introduced  with  the  air  into  the  generator. 
The  nitrogen  cools  -the  producer  gas  flame. 

Following  is  a  somewhat  more  exact  treatment  of  the  question 
if  it  seems  wise  to  the  teacher  to  take  it  up  with  the  class. 
The  average  volume  compositions  of  the  gases  in  question  are : 
Water  gas:  H2,  46;  CH4,  2;  CO,  46;  C02,  4;  N?,  2. 
Producer  gas:  H2,  12;  CEU,  1;  CO,  27;  C02,  3;  N2,  57. 


80 


COMPOUNDS  OF  CARBON 


100  volumes  of  water  gas  require  the  volumes  of  oxygen  and 
yield  the  volumes  of  product  as  shown  in  the  following  table : 


VOLUME  COMBUS- 
TIBLE COMPONENTS 

VOLUME  OXYGEN 
REQUIRED 

VOLUME  COMBUS- 
TION PRODUCTS 

H2 

46 

23 

46 

CH4 

2 

4 

6 

CO 

46 

23 

46 

94 

50 

98 

For  simplicity,  let  us  consider  that  air  contains  exactly  one 
volume  of  02  to  four  volumes  of  N2.  The  nitrogen  in  the  air  re- 
quired for  the  combustion  of  100  volumes  of  water  gas  has  a  volume 
of  4  x  50  =  200.  The  non-combustible  components  of  the  gas 
amount  to  6  volumes.  The  total  volume  of  gases  after  combustion 
is  thus  98  +  200  +  6  =  304. 

100  volumes  of  producer  gas  require  the  volumes  of  oxygen  and 
yield  the  volumes  of  products  as  shown  in  the  following  table : 


VOLUME  COMBUS- 
TIBLE COMPONENTS 

VOLUME  OXYGEN 
REQUIRED 

VOLUME  COMBUS- 
TION PRODUCTS 

H2 

12 

6 

12 

CH4 

1 

2 

3 

CO 

27 

13.5 

27 

40 

21.5 

42 

The  nitrogen  in  the  air  required  for  combustion  has  a  volume 
of  4  x  21.5  =  86.0.  The  non-combustible  components  of  the  gas 
amount  to  60  volumes.  The  total  volume  of  gases  after  combustion 
amounts  to  42  +  86  +  60  =  188. 

If  enough  producer  gas  is  taken  to  contain  94  instead  of  40  volumes 
of  combustible  gas,  thus  giving  as  much  combustible  as  contained  in 
the  100  volumes  of  water  gas,  the  total  volume  of  gases  after  com- 
bustion would  be  f  $  x  188  =  442. 


PAGES  282-298  81 

Then,  assuming  what  is  nearly  true,  that  the  heating  power  of 
equal  volumes  of  the  combustibles  in  each  gas  is  the  same,  we  see 
that  the  same  quantity  of  heat  will  have  to  raise  304  volumes  of 
gas  to  the  temperature  of  the  flame  in  the  case  of  water  gas  and 
442  volumes  of  gas  to  the  temperature  of  the  flame  in  the  case  of 
producer  gas.  Hence  the  temperature  attained  in  the  water  gas 
flame  will  be  higher. 

We  will  make  another  assumption,  which,  although  inaccurate, 
is  sufficiently  near  the  truth  to  serve  in  making  a  rough  estimate ; 
namely,  that  the  heat  capacity  of  equal  volumes  of  all  the  gases 
concerned  is  the  same.  With  the  same  amount  of  heat  available, 
then,  the  rise  in  temperature  in  the  flame  will  be  inversely  propor- 
tional to  the  volume  of  gases  that  must  be  heated.  If  the  feed  gas 
and  air  are  at  0°  C.,  the  centigrade  temperature  of  the  water  gas 
flame  would  be  f  |-f  or  1.45  times  as  high  as  that  of  the  producer  gas 
flame. 

It  is  the  common  practice  in  metallurgical  operations  where 
producer  gas  is  used,  to  preheat  to  a  high  temperature  the  feed  gas 
and  air  before  leading  them  into  the  combustion  chamber.  Thus 
a  much  higher  flame  temperature  is  attained. 

11.  See  Section  290,  p.  277, 

12.  See  Section  291,  p.  278. 

13.  See  Section  294,  p.  279. 


CHAPTER   XXIV 

COMPOUNDS    OF   CARBON   (Continued) 

Pages  282-298 

THIS  chapter  on  the  fundamentals  of  what  is  called  organic 
chemistry  is  especially  important  to  those  who  may  study  domestic 
science  later.  Considerably  more  may  be  given  by  the  teacher  in 
special  cases  where  the  maturity  and  special  needs  of  the  pupil  seem 
to  justify  it.  A  treatment  of  some  member  of  the  paraffin  series, 
showing  consecutively  the  hydrocarbon  itself,  its  alcohol,  its  alde- 
hyde and  its  acid,  will  be  useful  later  when  various  substances  such 


82  COMPOUNDS  OF  CARBON   (Continued) 

as  glycerine  (an  alcohol),  the  sugars  (some  have  aldehyde  struc- 
ture), acetic  acid  (having  the  COOH  group),  etc.,  are  studied. 
While  studying  the  chemistry  of  the  paraffin  series,  it  will  be  well 
to  go  a  little  more  at  length  into  the  matter  of  the  practical  sepa- 
ration of  petroleum  products  than  is  done  in  the  textbook.  The 
methods  of  the  oil  refineries  illustrate  splendidly  the  use  of  dis- 
tillation, of  fractional  distillation,  and  of  destructive  distillation.1 
The  use  of  destructive  distillation  at  increased  pressure,  in  order  to 
obtain  products  of  different  character  from  those  to  be  had  at  ordi- 
nary pressure,  may  be  brought  out,  and  in  this  connection  the 
matter  of  thus  increasing  the  amount  of  gasoline-like  product 
obtainable  from  a  given  crude  oil  is  of  great  importance  to  the 
automobile  industry. 

The  teacher  may  take  a  little  time  in  connection  with  the  study 
of  foodstuffs  to  inform  the  class  as  to  the  proper  balance  of  each 
type  of  food  in  a  well  ordered  diet,  and  also  to  take  up  the  method 
of  elimination  of  the  resulting  products  after  oxidation  in  the  body. 
It  should  be  shown  that  whereas  the  C02  and  H20  resulting  from 
the  oxidation  of  fats  and  carbohydrates  are  easily  eliminated  by 
lungs,  skin,  and  kidneys,  the  protein  is  less  completely  oxidized  in 
the  body  and  the  resulting  complex  substances  are  with  difficulty 
eliminated  by  the  body,  principally  through  the  kidneys.  If 
excess  of  protein  is  habitually  used  over  long  periods,  much  harm 
may  result  at  or  after  middle  life.  Boys  who  are  in  athletic 
training  will  be  found  especially  interested  in  this  matter.  In 
connection  with  the  discussion  of  alcohol,  a  valuable  lesson 
may  be  had  as  to  the  economic  waste  involved  in  the  chang- 
ing of  grain  products  into  alcoholic  beverages.  This  view  of 
the  matter,  as  developed  on  page  292,  may  have  more  force  with 
pupils  than  any  attempt,  along  the  usual  lines,  to  teach  them 
temperance. 

In  studying  soaps  pupils  may  themselves  make  up  small  samples 
of  very  good  soap  or,  better  yet,  the  work  may  be  done  as  a  class 
project. 

1  For  detailed  accounts  of  the  methods  in  use,  see :  Molinari,  Treatise  on 
General  and  Industrial  Chemistry,  P.  Blakiston's  Son  and  Company ;  or, 
Rogers  and  Aubert,  Industrial  Chemistry,  D.  Van  Nostrand  Company. 


PAGES  299-326  83 

Answers  to  Questions  on  Chapter   XXIV 

Page  298 

1.  See  Section  295,  p.  282,  especially  the  second  paragraph  on 
page  283. 

2.  See  Section  295,  especially  the  third  and  fourth  paragraphs 
on  page  283. 

3  and  4.    See  last  paragraph  on  page  283. 

5.  The  formulas  are  C18H38,  Ci0H22,  C5H12. 

6.  See  Section  298,  p.  286. 

7.  See  Section  300,  p.  288. 

8.  Glucose  is  a  common  name  for  a  product  consisting  largely  of 
grape  sugar. 

9.  Assume  that  glucose  is  entirely  grape  sugar. 

C6H1206  ->  2  C02  +  2  C2H5OH 
180  92.1 

180:92.1::  100  :x 

x  =51.2  grams  of  alcohol. 

10.  See  Section  304,  p.  291. 


CHAPTERS   XXV  AND  XXVI 

THE   IONIC    THEORY   AND    ELECTROLYSIS 

Pages  299-326 

IT  has  for  some  time  been  a  vexed  question  whether  the  subject 
of  ionization  should  or  should  not  be  included  in  an  elementary 
textbook  in  chemistry. 

It  seems  to  the  authors  that  this  great  extension  of  the  atomic 
theory  may  now  be  taught  to  beginners  in  chemistry  if  the  approach 
to  it  is  made  through  familiar  facts,  and  after  considerable  accumu- 
lation of  matter  that  can  be  satisfactorily  accounted  for  only  by 
means  of  this  theory.  This  would  naturally  throw  the  subject  late 
hi  the  course. 

To  secure  thorough  understanding  of  the  matter  every  pupil 


84  THE  IONIC  THEORY  AND  ELECTROLYSIS 

should,  if  possible,  be  given  an  opportunity  to  actually  electrolyze 
various  solutions.  Where  this  is  not  possible  a  lecture  table  demon- 
stration of  the  results  of  electrolyzing,  say,  hydrochloric  and  sul- 
phuric acids,  sodium  hydroxide,  and  sodium  sulphate  solutions, 
should  be  made.  Pupils  will  already  be  familiar  with  the  results 
of  the  electrolysis  of  H2S04  (Section  103,  p.  103)  and  of  HC1  (Sec- 
tion 141,  p.  136). 

Such  objective  demonstrations  as  that  in  which  the  concentra- 
tion of  sulphate  ion  about  the  positive  electrode  is  shown  to  be 
greater  than  elsewhere  in  the  cell  (Section  334,  p.  316),  are  very 
valuable  in  impressing  on  the  pupil  the  probable  reality  of  the 
existence  and  migration  of  ions. 

The  opportunity  which  these  chapters  on  the  ionic  theory  pre- 
sent, to  introduce  very  briefly  the  modern  view  of  the  atomic 
structure  of  electricity,  should  not  be  neglected.  Pupils  will  be 
found  to  be  wonderfully  receptive  to  the  beautifully  simple  modern 
conception  of  the  oneness  of  matter  and  of  energy.  The  teacher 
who  has  been  too  busy  to  follow  up  the  recent  advances  in  the 
literature  will  find  an  excellent  short  summary  of  the  matter  in 
the  little  book  Beyond  the  Atom.1  The  electrolysis  of  copper  sul- 
phate -(Section  339,  p.  320)  affords  an  opportunity  to  give  the  class 
a  glimpse  of  the  principles  underlying  electroplating.  If  any  of 
the  class  are  interested  in  art-metal  work,  the  actual  plating  of 
articles  of  copper,  to  cover  the  solder  used  in  making  them,  will 
prove  of  interest.  While  copper  sulphate  solution  can  be  made  to 
serve  for  this  purpose  by  properly  regulating  the  current,  an  alka- 
line cyanide  bath  will  be  found  easier  to  work  with.  On  account 
of  the  very  poisonous  character  of  such  cyanide  solutions  pupils 
should  not  be  allowed  to  work  with  them  unless  under  direct  super- 
vision. Very  slow  deposition  of  the  metal  gives  the  best  and 
most  adherent  coating,  and  the  surfaces  to  be  plated  must  of  course 
be  chemically  clean.  A  caustic  soda  solution  will  remove  grease, 
after  which  the  articles  should  be  rinsed  and  then  not  again  handled 
before  plating. 

Gold  and  silver  may  be  substituted  for  copper  if  desired,  the 
alkaline  cyanides  again  being  used. 

1  Cox,  Beyond  the  Atom,  G.  P.  Putnam's  Sons. 


PAGES  299-326  85 

Answers  to  Questions  on  Chapter  XXV 

Page  309 

1.  See  Sections  217,  312,  pp.  207,  299. 

2.  The  OH~  ion  is  the  component  common  to  all  bases.     Hence 
it  must  be  the  component  which  turns  litmus  blue.     Likewise  it 
must  be  the  H+  ion,  the  common  component  of  all  acids,  which 
turns  litmus  red. 

3.  At  ordinary  temperatures  pure  substances  (other  than  un- 
combined  metals)  are  not  ionized,  hence  do  not  conduct  the  elec- 
tric current.     Dissolved  in  water  (also  in  a  number  of  other  sol- 
vents, among  which  alcohol  and  anhydrous  liquid  ammonia  are 
conspicuous)  acids,  bases,  and  salts  become  in  some  way  separated 
into  ions  and  thus  become  conductive.     Note.   The  theory  as  ordi- 
narily stated  and  used  would  convey  the  impression  that  ions  were 
single  atoms  or  radicals  bearing  electric  charges.     It  is  principally 
on  account  of  our  ignorance  of  the  true  magnitude  of  the  ions,  that 
we  in  a  measure  dodge  the  question  by  writing  the  simple  formulas 
which  we  customarily  use  for  the  ions.     As  a  matter  of  fact  we 
have  a  good  deal  of  evidence  that  ions  have  attached  to  them  con- 
siderable amounts  of  the  solvent,  just  as  copper  sulphate  holds  in 
combination  five  molecules  of  water  of  crystallization  in  blue  vitriol, 
CuS04  •  5  H20.     Since  we  do  not  know  much  about  the  amount  of 
water   thus   combined  with  the   ions,  we   are   prone  to   ignore  it 
altogether  and  thus  give  a  rather  wrong  impression  to  our  pupils.    It 
is  well  to  discuss  this  matter  in  classroom,  comparing  the  probable 
hydration  of  the  ions  with  that  of  salts  that  crystallize  with  water. 

4.  See  Section  325,  p.  305.     In  solutions  containing  each  one 
mole  of  acid  in  10  liters  of  water  only  0.1  per  cent  of  the  carbonic 
acid  is  ionized  (H2C03  ±£  H+  +  HC03~)  whereas  60  per  cent  of 
the  sulphuric  acid  is  ionized  (H2S04  ±£  2  H+  +  SO4— ). 

6.  See  Section  323,  p.  305.  Note.  Of  course  the  teacher  may 
here  cite  as  proofs  of  the  ionic  theory  the  phenomena  of  vapor  pres- 
sure lowering,  osmotic  pressure,  freezing  point  lowering,  and  boil- 
ing point  raising,  all  of  which  effects  are  proportional  to  the  num- 
ber of  moles  of  dissolved  substance  in  the  solution  and  altogether 
independent  of  the  kind  of  substance.  In  ionized  substances  it 


86  THE  IONIC  THEORY  AND  ELECTROLYSIS 

appears  as  if  each  separate  ion  produced  just  as  much  effect  as  an 
entire  undissociated  molecule.  Hence  by  determining  how  much 
one  of  these  effects  produced  by  a  dissolved  electrolyte  exceeds  the 
effect  that  would  be  calculated  on  the  assumption  of  there  being 
no  ionization,  one  has  a  means  of  estimating  the  number  of  ions 
present.  These  considerations  if  clearly  presented  are  in  no  wise 
beyond  the  comprehension  of  the  pupil,  but  they  involve  so  many 
entirely  new  ideas  that,  if  they  are  to  be  given  well  enough  to  be 
worth  while,  altogether  too  much  time  must  be  devoted  to  them. 
Furthermore  their  connection  with  the  common  experiences  of  the 
pupil  or  with  the  rest  of  the  elementary  study  of  chemistry  is  too 
remote  to  warrant  the  use  of  so  much  time.  Hence  in  the  textbook 
the  development  of  the  ionic  theory  is  based  entirely  on  the  electrical 
conductivity  and  the  great  reactivity  of  electrolytes. 

6.  K+  +  OH-  +  H+  +  Cl-   ->    K+  +  C1-+  H20 

2  Na+  +  2  OH'  +  2  H+  +  S04"  ->  2  Na+  +  S04~  +  2  H20 
2  K+  +  2  OH-+  2  H+  +  S04~  ->  2  K+  +  SO4"  +  2  H20 
Ca++  +  2  OH'  +  2  H+  +  2  Cl~  -*  Ca++  +  2Cl-  +  2H20 
Ca++  +  2  OH-  +  2  H+  +  S04"  ->  Ca+4  +  SO4"+  2  H20 
and  since  CaS04  is  only  sparingly  soluble, 

Ca++  +  S04~  ±£  CaS04|. 

In  Section  233,  NH4OH  is  characterized  as  a  mild  alkali,  which 
would  indicate  that  it  gives  comparatively  few  OH"  ions.  There- 
fore, before  all  of  this  base  can  be  neutralized,  it  must  progressively 
become  ionized  to  keep  resupplying  the  deficiency  caused  by  the 
removal  of  OH"  ions  in  the  formation  of  water.  This  progressive 
ionization  and  neutralization  takes  place  with  extreme  rapidity, 
and  the  neutralization  of  a  weak  base  is  thus  not  measurably  slower 
than  that  of  a  strong  base, 

2  NH4OH  ^±  2  NH4+  +  2  OH~ 
S04~  +  2  H+ 

2H2O 
NH4OH   ±£  NH4+  +  OH- 

Cl-  +  H+ 


[20 
K+  +  OH-  +  H+  +  N03~  ->  K+  +  N03~  +  H20 


PAGES  299-326  87 

7.  Ag+  +  NOr  +  H+  +  Cl-  ->H+  +  N03-  +  AgClj 

2  Ag+  +  S04~  +  2  K+  +  2  Cl-   ->2  K+  +  S04~  +  2  AgCl| 

8.  Ba++  +  2  Cl-  +  2  Na+  +  S04~  ->  2  Na+  +  2  Cl~  +  BaS04 1 
:Ba++  +  2  OH-  +  2  H+  +  S04~  ->  2  H20  +  BaS04  t 

9.  Na+  +  OH"  +  H+  +  N(V  ->  Na+  +  N03-  +  H20 
NH4+  +  Cl-  +  Na+  +  N03-        ->  no  change 

K+  +  NOr  +  Na+  +  Cl-  ->•  no  change 

NH4+  +  Cl-  +  Na+  +  OH"  ±£    Na+  +  Cl~  +  NH4OH 

(not  entirely  complete) 
NH4OH  ±^  NH4+  +  OH- 
Cl-  +  H+ 

H20 

The  vertical  reaction  in  this  method  of  presentation  is  so  com- 
plete that  the  OH"  ion  shown  on  the  right  hand  side  of  the  hori- 
zontal reaction  has  no  chance  to  accumulate  in  the  solution.  With- 
out such  an  accumulation  this  reaction  finds  no  opposition,  and 
proceeds  to  completion  towards  the  right,  in  spite  of  the  fact  that 
its  tendency  to  proceed  in  this  direction  is  small,  corresponding 
to  an  ionization  of  NH4OH  of  only  about  1  per  cent  in  pure  water. 

Note.  It  will  be  noted  that  the  usage  is  adopted  in  the  fore- 
going, of  letting  all  salts  and  the  strong  acids  and  bases  appear  in 
reactions  as  completely  ionized.  This  is  an  entirely  justifiable 
practice. 

Nothing  said  in  the  textbook  up  to  this  point  necessitates  writing 
the  reactions  for  NH4OH  different  from  those  for  NaOH,  and  the 
teacher  may  prefer  not  to  dwell  on  this  difference. 

Answers  to  Questions  on  Chapter  XXVI 

Page  326 

1.  See  Sections  315, 320,  pp.  301, 303.  In  electrolytic  conduction, 
the  electricity  passes  through  the  solution  only  as  it  is  carried  in 
definite  amounts  on  the  atoms  and  radicals  which,  with  these 
charges,  we  call  ions.  In  metallic  conduction  there  is  no  move- 
ment of  material  atoms,  but  the  electricity  must  pass  from  atom 


88  THE  IONIC  THEORY  AND  ELECTROLYSIS 

to  atom.  Note.  In  Section  331,  p.  314,  it  was  stated  that  the 
negative  electrons  are  known  to  exist  independent  of  ordinary 
matter,  whereas  the  positive  electrons,  if  such  exist  at  all,  are  never 
found  separate  from  material  atoms.  It  is  easy  to  see  that  positive 
ions  would  result  from  atoms  of  metals  if  each  lost  these  little  nega- 
tive electrons,  which  must  be  able  to  escape  more  easily  than  posi- 
tive electrons.  These  negative  electrons  can  pass  to  atoms  of  non- 
metals,  like  Cl,  and  attach  themselves  thereto,  forming  negative  ions. 
In  a  metallic  mass,  the  metal  atoms  can  all  part  easily  with  nega- 
tive electrons,  but  there  are  no  atoms  of  non-metals  at  hand  to 
attach  and  hold  these  electrons.  Hence  negative  electrons  are  free 
to  pass  from  atom  to  atom  or  possibly  around  among  the  atoms  in 
a  mass  of  metal.  Non-metals,  on  the  other  hand,  cannot  be  con- 
ductors, because  from  their  inability  to  form  positive  ions,  we  know 
that  they  are  not  able  to  part  with  any  of  their  normal  complement 
of  negative  electrons.  It  is  true  that  their  ability  to  form  negative 
ions  might  be  ascribed  not  to  ability  to  attach  extra  negative  elec- 
trons, but  to  ability  to  lose  some  of  their  normal  complement  of 
positive  electrons.  These  positive  electrons,  however,  we  have 
just  said  are  only  known  associated  with  material  particles  of  the 
magnitude  of  the  atoms ;  hence,  if  they  escaped  from  non-metal 
atoms,  they  would  not  be  able  to  move  around  freely  in  the  mass 
of  non-metal  as  do  the  very  small  negative  electrons  in  the  mass 
of  metal. 

2.  See  Section  329,  p.  312. 

3.  If  dilute  H2S04  were  electrolyzed  for  a  very  long  time,  the 
solution  would  become  more  concentrated,  since  only  water  is  de- 
composed, all  the  H2S04  being  regenerated  at  the  positive  electrode. 
It  should  be  noted  that  a  very  prolonged  electrolysis  would  be 
necessary  to  produce  much  effect  of  this  kind,  for  96,600  coulombs 
are  necessary  to  decompose  9  grams  of  water  (a  current  of  1  ampere 
would  have  to  flow  96,600  seconds,  or  27  hours,  to  give  this  number 
of  coulombs). 

4.  See  Section  332,  p.  315.     If  the  S04"  ion  is  really  discharged 
at  the  +  electrode  during  electrolysis,  the  free  S04  radical  must  at 
once  react  with  water,  regenerating  H2S04  and  liberating  oxygen. 
Note.     It  is  in  some  ways  a  simpler  assumption  and  one  which  is 


PAGES  299-326  89 

doubtless  closer  to  the  truth  to  say  that  the  SO*  ions  do  not  dis- 
charge at  all,  but  that  water  dissociates  to  an  infinitesimal  extent, 
(H20^2H++O~).  The  O~  ions  nearest  the  electrodes  dis- 
charge, leaving  the  H+  ions  balanced  by  the  S04~~  ions  brought  up 
by  the  current.  Since  water  can  continue  to  ionize  to  an  infinitesi- 
mal extent  to  make  up  for  the  0"  ions  discharged,  this  process  can 
continue  indefinitely. 

6.  See  Section  336,  p.  318.  Note.  As  with  the  SO4~  ion,  we  do 
not  need  to  suppose  that  the  Na+  ion  is  really  discharged.  The  H+ 
ions  furnished  by  the  slight  dissociation  of  water,  (H20^ 
H+  +  OH~),  can  discharge  instead,  and  the  water  in  the  immediate 
neighborhood  of  the  electrode  will  continue  to  ionize  always  to  a 
slight  extent  to  make  up  for  the  H+  ions  discharged.  The  OH" 
ions  which  thus  accumulate  through  the  continuous  dissociation  of 
water,  remain  near  the  —  electrode  balanced  by  the  Na+  ions  which 
are  brought  up  by  the  current.  That  it  is  possible  to  discharge  Na+ 
ions  is  shown  in  the  electrolysis  of  molten  NaOH  (Section  336,  p. 
318),  and  also  in  the  electrolysis  of  a  Na  salt  solution  with  a  mer- 
cury electrode  in  which  latter  the  discharged  Na  dissolves  to  form 
an  amalgam. 

6.  See  Section  334,  p.  316. 

7.  See  Sections  337,  342,  pp.  319,  322.     It  is  of  course  obvious 
that  the  charges  on  2  Na+  ions  are  exactly  equivalent  to  the  charges 
on  one  S04"  ion,  since  the  whole  solution  of  Na2S04  shows  no  elec- 
trification.    Likewise  after  the  electrolysis  has  proceeded  some 
time,  since  the  solution  shows  still  no  electrification,  it  is  obvious 
that  just  as  much  +  electricity  must  have  been  discharged  at  the 
-  electrode   as    of  -  electricity   at   the    +  electrode.      Therefore 
2  Na+  ions  must  discharge  for  every  S04      ion.     A  glance  at  the 
secondary  reactions    shows  that  2  NaOH  must    result  for  every 
H2S04  formed,  and  these  are  quantities  of  the  acid  and  base  which 
will  just  neutralize  each  other. 

8.  Metals  which  stand  high  in  the  order  of  activity  (see  table  on 
page  235,  or  the  more  complete  table  on  page  329)  would  be  unlikely 
to  deposit  on  the  -  electrode  during  the  electrolysis  of  solutions  of 
their  salts.     Since  H  is  less  active  and  since  even  water  contains 
some  H+  ions,  hydrogen  will  discharge  by  preference.     Of  course 


90  THE  ELECTROMOTIVE  SERIES 

the  metals  like  lead  and  tin,  which  are  only  a  little  more  active  than 
hydrogen,  are  more  likely  to  be  deposited  than  the  metals  higher  up, 
and  we  must  bear  in  mind  that  water  furnishes  but  a  small  concen- 
tration of  H  +  ions,  whereas  salts  of  Pb  and  Sn  furnish  a  high  con- 
centration of  Pb++  and  Sn++  ions.  Metals  standing  below  hydro- 
gen in  the  order  of  activity  would  always  deposit  in  preference  to 
hydrogen  on  the  —  electrode. 

9.  Any  metal  standing  below  hydrogen  in  the  order  of  activity 
can  be  electroplated  on  a  conducting  object  which  is  made  the  — 
electrode,  when  a  solution  of  the  salt  of  the  metal  is  electrolyzed. 
(See  Electroplating  of  Copper,  Section  340,  p.  321.) 

10.  A  useful  device  for  measuring  the  passage  of  the  electric 
current  is  to  make  the  circuit  pass  through  a  cell  with  two  copper 
electrodes  and  a  solution  of  a  copper  salt.    For  every  31.8  grams  of 
copper  deposited  on  the  —  electrode  and  dissolved  from  the  +  elec- 
trode, the  amount  of  electricity  which  has  passed  is  96,600  coulombs. 
Of  course  other  metals  and  metal  salts  may  be  used,  and  we  find  for 
example  that  108  grams  of  silver  is  equivalent  to  the  31.8  grams  of 
copper. 

11.  From  the  formulas  of  the  ions  Cu++  and  Ag+  it  is  seen  that 
one  copper  ion  is  electrically  equivalent  to  two  silver  ions.     There- 
fore 63.6  grams  of  copper  would  be  equivalent  to  2x1 08  =  216 
grams  of  silver  and  6.36  grams  of  Cu  would  be  equivalent  to  21.6 
grams  of  Ag  =  weight  of  silver  which  would  be  deposited. 

12.  2  A1+++  is  electrically  equivalent  to  3  Cu++. 

2  X  27.1  g.  Al  are  equivalent  to  3  X  63.6  g.  Cu. 
Therefore  27.1  g.  Al  are  equivalent  to  f  X  63.6  =  95.4  g.  Cu. 

CHAPTER  XXVII 

THE   ELECTROMOTIVE    SERIES 

Pages  327-332 

THE  order  in  which  the  metals  stand  according  to  the  electro- 
motive series  has  already  been  hinted  at  several  times,  not  only  in 
the  chapters  on  the  ionic  theory  and  on  electrolysis,  but  also  pre- 


PAGES  327-332  91 

viously  when  the  metals  were  rated  in  the  order  of  their  chemical 
activity  (Section  252,  p.  235).  The  fact  that  this  difference  in 
activity  is  related  to  the  degree  to  which  the  metals  possess  elec- 
tropositive character  can  now  be  brought  out.  The  Displacement 
of  acid  hydrogen  by  the  more  active  metals  can  now  also  be  related 
to  the  position  of  hydrogen  in  the  electromotive  series.  The  fact 
that  hydrogen,  when  condensed  on  platinum,  can  displace  copper 
from  solution  and  cause  it  to  be  deposited  on  the  platinum,  may 
be  advanced  as  further  proof  of  hydrogen's  title  to  a  position  above 
copper  in  the  ranks  of  the  metals. 

Answers  to  Questions  on  Chapter  XXVII 

Page  332 

1.  In  a  mass  of  copper  metal  the  atoms  are  electrically  neutral 
and  therefore  possess  no  electrostatic  repulsion  or  attraction  for 
each  other.     The  natural  cohesion  of  the  Cu  atoms  for  each  other 
has  an  opportunity  to  exert  itself,  and  this  accounts  for  the  com- 
pactness and  tenacity  of  a  piece  of  copper.     In  a  solution  of  a 
copper  salt,  on  the  other  hand,  every  copper  atom  has  negative 
electrical  charges,  and  since  like  charges  repel  each  other,  there  is 
no  chance  for  the  copper  atoms  to  cohere. 

2.  Fe°  +  Cu++  +  S04~->  Fe++  +  S04~  +  Cu°. 

The  sign  °  is  used  to  draw  attention  to  the  fact  that  the  atoms  so 
designated  bear  no  charges. 

3.  See  Section  348,  p.  329. 

4.  See  Sections  242,  243,  pp.  226,  227  and  Section  348,  first  sen- 
tence, p.  329.    The  most  important  chemical  characteristic  of  metals 
is  their  ability  to  form  simple  positive  ions,  and  this  characteristic 
is  shown  to  a  marked  degree  by  hydrogen. 

5.  At   ordinary  temperatures   chemical   reactions   among  non- 
ionized  substances  are  for  the  most  part  so  slow  that  they  can 
almost  be  said  not  to  take  place  at  all.     Now  water  is  ionized  to  a 

very  slight  extent,  of  a  mole  being  ionized  into  H+  and 


OH~  ions  in  every  liter  of  pure  water.     Of  course  it  is  obvious  that 
the  more  active  a  metal  is,  the  more  vigorously  it  will  drive  out 


92  THE  ELECTROMOTIVE  SERIES 

even  the  few  H+  ions  in  pure  water.  Sodium,  potassium,  and  cal- 
cium therefore,  being  among  the  most  active  metals,  are  the  most 
able  to  set  hydrogen  free  from  water.  Water  has  the  ability,  like 
all  substances  capable  of  ionization,  of  rapidly  dissociating  to  re- 
supply  any  ions  that  are  taken  away,  and  so  the  displacement  of 
ionic  hydrogen  may  continue  until  the  -active  metal  is  all  exhausted. 
Metals  like  magnesium,  aluminium,  and  zinc,  are  active  enough  to 
displace  hydrogen,  but  here  the  metal  ions  form  insoluble  hydroxides 
with  the  OH"  ions  likewise  furnished  by  the  dissociation  of  water. 
These  hydroxides  adhere  to  the  metal  surface  and  protect  it  from 
any  continued  action. 

6.  (1)  Fe°  +  Cu++       -*Fe++   +  Cu° 

55.8  63.6 

(2)  Zn°  +  Cu++  ->  Zn++  +  Cu° 
65.4  63.6 

(3)  Mg°  +  Cu++  ->  Mg  ++  +  Cu° 
24.3  63.6 

(4)  2  Al°  +  3  Cu++  ->    2  A1+++   +  3  Cu° 
2x27.1  3X63.6 

(1)  55.8 :  63.6 : :  56 :  x  x  =  63.8  grams  of  Cu 

(2)  65.4 :  63.6 : :  65 :  x  x  =  63.2  grams  of  Cu 

(3)  24.3 :  63.6  : :  24 :  x  x  =  62.8  grams  of  Cu 

(4)  54.2 :  190.8 : :  27 :  x  x  =  95  grams  of  Cu    ^~ 

7.  (a)  Zn°  +  2  H+  +  2  Cl~  ->  Zn++  +  2  Cl~  +  H2° 
(6)  Zn°  +  Cu++  +  2  Cl-  -+  Zn++  +  2  Cl~  +  Cu° 

(c)  Zn°  +  2  Ag+  +  2  NOr      ->  Zn++  +  2  NOr  +  2  Ag° 

(d)  2  Al°  +  3  Hg++  +  6  NOr  ->  2  Al  +++  +  6  N03-  +  3  Hg° 

(e)  Fe°  +  AU+++  +  3  Cl-        -*  Fe  +++  +  3  Cl~  +  Au° 
(/)  Cu°  +  Zn++    +  2  Cl~         ->  no  change 

(g)  Cu°  +  2  H+  +  2  Cl-  ->  no  change 

(h)  Cu°  +  2  Hg+  +  2  N03-  ->  Cu++  +  2  N03-  +  2  Hg° 

(i)  Cu°  +  Hg++  +  2  NOr  ->  Cu++  +  2  NOr  +  Hg° 

(/)  2  Cu°  +  Pt++++  +  4  Cl-  ->.  2  Cu++  +  4  Cl-  +  Pt° 

(A)  3  Ag°  +  AU+++  +  3.  CL-  ->  3  AgCty  +  Au° 

(0  4  Ag°  +  R++++  -h  4  Cl-  ->  4  AgCH  +  Ptc 


o 


PAGES  333-341  93 


CHAPTER  XXVIII 

HYDROGEN    EQUIVALENTS    AND    VALENCE 

Pages  333-341 

IF  pupils  are  given  an  opportunity  to  actually  perform  the  ex- 
periment which  is  described  in  Section  353,  p.  333,  especially  if  it 
is  done  for  two  different  metals  of  different  valences,  as,  for  example, 
with  magnesium  and  with  aluminium,  no  difficulty  should  be  ex- 
perienced in  giving  them  thorough  comprehension  of  the  meaning 
of  hydrogen  equivalents.  Through  that  comprehension,  a  much 
more  real  grasp  of  the  significance  of  valence  may  be  had  than  was 
possible  when  that  topic  was  first  introduced  in  Section  215,  p.  203. 
The  teacher  should  also  perform  a  similar  experiment  with  metallic 
sodium  to  illustrate  the  case  of  a  monovalent  element. 

Most  pupils  will  need  the  triple  repetition  of  the  calculation  before 
they  will  thoroughly  understand  just  what  they  are  after  and  just 
why  they  do  the  various  things  in  the  calculation.  When  the  three 
hydrogen  equivalents  are  before  them,  they  can  then  compare 
them  with  the  three  atomic  weights  (Na,  Mg,  and  Al).  The  facts 
that  the  two  numbers  are  about  the  same  for  sodium,  while  the 
hydrogen  equivalent  of  Mg  is  about  ^  the  atomic  weight,  and  that  of 
Al  is  about  J,  will  at  once  appear.  It  is  then  easy  to  lead  the  pupil 
to  see  that  the  displacement  of  hydrogen  by  sodium  must  have 
been  an  atom  for  atom  displacement,  and  that  the  valence  of  Na 
is  I,  whereas  each  atom  of  Mg  must  have  displaced  2  atoms  of 
hydrogen  and  each  Al  atom  must  have  displaced  3  of  hydrogen, 
making  the  valence  of  Mg  II  and  that  of  Al  III. 

Answers  to  Questions  on  Chapter  XXVIII 
Page  341 

1.  See  Section  352,  p.  333. 

2.  Multiply  the  number  of  liters  at  standard  conditions  by  .09. 
See  Section  353,  top  of  p.  335. 


94  SULPHUR 

070        740 
3.   24.4  c.c.  of  H2at  20°  and  740  mm.  =  24.4  X  .|g|  X  jjj-  -  22.1 

c.c.  under  standard  conditions. 

22  1 
Weight  of  hydrogen  =  X  0.09  =  0.00199  gram. 


0.112  gram  of  Cd  is  equivalent  to  0.00199  gram  of  H. 

i  oo 
Weight  of  Cd  equivalent  to  1  gram  of  H  =  Q  X  0.112  =  56.3 


grams. 

Hydrogen  equivalent  of  cadmium  =  56.3  grams. 
4.   The  valence  of  cadmium  is  2. 

6.  It  would  be  well  to  plan  to  collect  about  80  c.c.  of  the  gas  if 
the  gas  measuring  tube  has  a  volume  of  100  c.c.  The  reaction 
would  be 

Zn  +  2HCl->ZnCl2  +  H2 
65  g.  22.4  1. 

80 
Weight  of  Zn  necessary  to  yield  80  c.c.  of  H2  =  22466  X  65  =  0.232 

gram. 

CHAPTER  XXIX 

SULPHUR 

Pages  342-357 

THIS  chapter,  while  hi  its  first  part  purely  descriptive,  leads  to 
the  consideration  of  the  important  practical  application  of  chemistry 
in  the  manufacture  of  sulphuric  acid. 

Teachers  should  emphasize  the  enormous  commercial  uses  of 
sulphuric  acid.  The  value  of  the  annual  output  is  almost  unbe- 
lievable, $22,000,000  in  1913  in  the  United  States  alone.  It  has 
been  said  that  there  is  no  article  used  by  civilized  man  which  has 
not  had  sulphuric  acid  used,  directly  or  indirectly,  in  connection 
with  its  making.  Perhaps  this  statement  will  seem  extravagant, 
but  on  being  thought  over  carefully  the  statement  will  be  found 
hard  to  contradict. 

Both  the  contact  process  and  the  chamber  process  are  described, 


PAGES  342-357  95 

as  they  are  both  likely  to  be  used  for  many  years,  the  chamber 
process  appearing  to  be  secure  against  the  competition  of  its  simpler 
rival  where  the  manufacture  of  impure  acid  is  concerned.  The 
nature  of  the  reactions  in  the  chamber  process  has  not  of  course  been 
gone  into  extensively,  as  the  possible  reactions  are  too  numerous 
and  too  complicated  for  discussion  in  an  elementary  textbook  and 
many  of  them  are  still  in  dispute.  The  essential  reactions  are 
given. 

Wherever  possible,  pupils  should  be  taken  to  see  a  sulphuric  acid 
plant.  Many  large  fertilizer  companies  have  their  own  acid  plants 
and  use  the  acid  in  making  phosphate  fertilizers.  Trips  to  such 
plants  will  afford  interesting  opportunities  for  the  study  of  the 
practical  application  of  chemistry.  Stereopticon  views  may  be 
made  to  serve  where  a  trip  is  impossible. 

Answers  to  Questions  on  Chapter  XXIX 

Page  356 

1.  Sulphur  is  distinctly  a  non-metal.     The  first  and  most  im- 
portant classification  of  the  elements  is  into  metals  and  non- 
metals. 

2.  The  oxides  of  sulphur  yield  acids  on  union  with  water. 

3.  See  Section  363,  p.  342. 

4.  See  Section  367,  p.  347,  last  paragraph. 

5.  Of  the  non-metallic  elements,  oxygen,  chlorine,  and  sulphur, 
sulphur  is  the  weakest,  that  is  to  say,  it  is  the  least  active  chemically 
towards  the  metals  and  hydrogen.     Oxygen  and  chlorine  combine 
with  violence  with  hydrogen,  sulphur  with  difficulty  (Section  366, 
p.  346).     Furthermore,  both  oxygen  and  chlorine  displace  sulphur 
from  solutions  of  H2S  or  of  the  sulphides 

2  H2S  +  02  -»  2  H20  +  2  S|. 
Here  the  sulphur  appears  as  a  milky  precipitate, 

Na2S  +  C12  ->  2  NaCl  +  S. 

In  this  case  sulphur  may  stay  in  solution  as  a  yellow  polysulphide, 
Na2S  •  S.C  (x  being  any  number  between  1  and  4  inclusive),  so  long  as 
excess  of  Na2S  is  present.  After  that  a  precipitate  may  be  seen, 
but  this  disappears  with  excess  of  chlorine  because  it  is  oxidized  to 


96  SULPHUR 

sulphuric  acid.  The  sulphides  of  the  heavy  metals  can  be  changed 
to  oxides  or  chlorides  by  roasting  in  air  or  roasting  with  salt  (see 
Chap.  XXII). 

6.  Sulphur  dioxide  and  oxygen  have  a  strong  enough  tendency  to 
combine,  but  the  reaction  is  extremely  sluggish  when  no  other  sub- 
stance is  present.     With  catalyzers,  the  reaction  is  facilitated  and 
its  natural  tendency  to  take  place  exerts  itself,     (a)  In  the  contact 
process,  finely  divided  platinum  acts  as  the  catalyzer.     (6)  In  the 
chamber  process,  oxides  of  nitrogen  act  as  the  catalyzer. 

7.  Concentrated   sulphuric   acid   is    appreciably   heavier   than 
concentrated  hydrochloric  acid,  and  it  is  a  good  deal  more  viscous,  so 
by  lifting  the  bottle  and  giving  it  a  rocking  motion  one  can  decide 
which  of  these  acids  it  contains.     If  the  stopper  is  removed,  HC1 
gas  escapes  in  the  one  case  and  can  be  perceived  by  the  odor  and  by 
the  mist  if  the  breath  is  blown  across  the  mouth.     H2S04  is  not 
volatile  and  gives  no  odor  or  mist. 

8.  In  1913,  3,000,000  tons  of  sulphuric  acid,  valued  at  $22,000,000, 
were  manufactured  in  the  United  States. 

9.  Rhombic,  monoclinic,  and  amorphous  sulphur  are  different 
forms  of  pure  sulphur,  just  as  ordinary  oxygen  and  ozone  are  differ- 
ent forms  of  pure  oxygen. 

10.  See  Sections  377  and  303,  pp.  354  and  290.     Concentrated 
sulphuric  acid  will  give  wood  a  charred  appearance. 

11.  4  FeS2  +  11  02  ->  2  Fe203  +  8  S02 
8  S02  +  4  02  +  8  H20  -*  8  H2S04 

1  mole  FeS2  yields  2  moles  H2S04 
120  196.2 

120 :  196.2 : :  1000 :  x 
x  =  1635  kilos  H2S04. 

12.  From  the  first  equation  under  11  we  see  that 
4  moles  of  FeS2  yield  8  moles  of  S02, 

or  1  mole  of  FeS2  yields  2  moles  of  S02 

120  kilos  (2  X  22.4  X  1000)  liters  =44.8  cubic  meters 

120 :  44.8 : :  1000 :  x 
x  =  373  cubic  meters  of  SO2. 

13.  See  Section  377,  p.  354. 

14.  Ammonia    combines   with   sulphuric   acid  to  form  a  salt, 


PAGES  358-376  97 

(NH4)2S04,  hence  ammonia  gas  cannot  be  dried  by  bubbling  it 
through  sulphuric  acid.  It  can  be  dried  with  lumps  of  CaO  or 
NaOH. 


CHAPTER  XXX 

COMPOUNDS    OF   NITROGEN 

Pages  358-376 

THE  study  of  nitrogen  compounds  affords  many  very  interesting 
and  practical  applications  of  chemistry,  especially  in  connection  with 
the  fixing  of  atmospheric  nitrogen  by  artificial  means,  and  also  in 
connection  with  the  use  of  nitrogen  compounds  as  explosives.  The 
chemistry  of  nitric  acid  is  more  complicated  than  that  of  sulphuric 
acid,  hence  it  is  given  only  in  this  later  part  of  the  course. 

The  fixing  of  nitrogen  by  active  metals  may  be  illustrated  in  the 
laboratory  by  the  use  of  Mg  powder  in  a  crucible.  On  being  heated, 
the  surface  material  changes  mainly  to  oxide,  but  much  of  the  in- 
terior powder  becomes  nitride.  The  ammonia  formed  when  the 
product  is  moistened  can  be  detected  by  its  odor.  This  experi- 
ment can  be  performed  quantitatively,  the  ammonia  being  re- 
leased into  HC1  solution  to  form  the  chloride.  If  standard  HC1 
be  taken,  the  residue  can  be  titrated  with  standardized  NaOH  and 
the  amount  of  ammonia  obtained  can  be  calculated. 

In  connection  with  the  study  of  ammonia,  visits  to  gas  plants 
where  ammonia  is  one  of  the  by-products,  should  by  all  means  be 
made  wherever  practicable.  An  artificial  ice  plant  which  uses 
ammonia  should  also  be  visited  by  the  class  if  possible.  Where 
such  trips  cannot  be  taken,  the  stereopticon  will  serve  to  help  make 
the  processes  clear. 

The  reactions  of  nitric  acid  with  metals  should  be  broadly  ex- 
plained as  in  Section  390-391,  pp.  366-370,  which  simplifies  the  other- 
wise seemingly  complicated  subject.  The  fact  that  sulphuric  acid 
acts  in  a  somewhat  similar  fashion  when  hot  (Section  390,  p.  368), 
illustrates  the  resemblance  between  the  two  acids  in  respect  to  their 
being  oxidizing  agents  as  well  as  acids. 


98  COMPOUNDS  OF  NITROGEN 

Pupils  will  need  some  help  in  assimilating  the  idea  that  the  addi- 
tion of  H  is  reduction  just  as  much  as  is  the  removal  of  a  non-metal 
like  oxygen  or  chlorine  (Section  391,  p.  368).  The  electrical  ex- 
planation of  the  matter  will  help  here  if  the  teacher  cares  to  develop 
that  point  of  view:  Increase  of  the  positive  valence  of  an  element 
or,  what  is  equivalent,  decrease  of  the  negative  valence,  consti- 
tutes oxidation.  Decrease  of  positive  valence,  or  increase  of  nega- 
tive valence,  constitutes  reduction.  For  example,  when  oxygen  is 
removed  from  N205  the  nitrogen  is  reduced,  for  the  positive  valence 
is  lowered  from  V  to  0.  When  hydrogen  is  added  to  the  nitrogen 
in  forming  NH3,  the  nitrogen  is  further  reduced,  for  the  negative 
valence  is  increased  from  0  to  III,  which  is  equivalent  to  lowering 
the  positive  valence  from  0  to  —  III. 

Great  interest  is  always  manifested  by  pupils  in  the  chemistry  of 
explosive  substances,  and  frequently  teachers  find  it  necessary  to 
interfere  tactfully  with  unwise  experimentation  on  the  part  of  pupils 
with  dangerous  substances. 

The  nitrogen  cycle  in  nature  will  require  some  classroom  discus- 
sion, and  specimens  of  sweet  clover  or  other  leguminous  plants  show- 
ing the  nodules  on  the  roots  should  be  exhibited  to  the  class.1 

Answers  to  Questions  on  Chapter  XXX 

Page  375 

1.  When  powdered  magnesium  is  heated  in  a  crucible,  a  chemical 
reaction  with  the  air  soon  takes  place  ;  the  oxygen  combines  with  the 
magnesium  of  the  upper  layers  so  that  only  the  more  abundant 
nitrogen  penetrates  to  the  lower  layers.     After  the  crucible  has 
been  heated  one  half  to  one  hour,  it  is  found  that  the  upper  one 
fifth  of  the  contents  is  mostly  magnesium  oxide  and  approximately 
the  lower  four  fifths  is  magnesium  nitride.     This  reacts  violently 
with  water  according  to  an  equation  similar  to  that  at  the  top  of 
p.  359. 

2.  See  Section  382,  p.  360. 

1  See  Knox,  The  Fixation  of  Atmospheric  Nitrogen,  D.  Van  Nostrand  and 
Company. 


PAGES  358-376  99 

3.  A  gas  which  by  itself  is  colorless  but  turns  brown  on  coming 
in  contact  with  the  air  must  be  nitric  oxide,  NO. 

4.  Zinc  stands  above  hydrogen  in  the  electromotive  series  and  it 
can  set  hydrogen  free  from  hydrochloric  acid.     Copper  stands  below 
hydrogen  in  the  series  and  cannot  displace  it  from  acids.     Thus 
HC1  is  without  action  on  Cu  (Section  348,  p.  329).     But  HN03 
is  an  oxidizing  agent  and  oxidizes  copper  to  CuO.     The  latter  being 
a  basic  oxide  reacts  with  more  of  the  acid  to  form  a  salt.     (See  Sec- 
tions 387,  390,  pp.  364,  366.) 

6.  2  HN03  ->  H2O  +  2  NO  +  3  0 

3  0  +  6  Ag  ->  3  Ag20 

3  Ag20  +  6  HN03  ->  3  H20  +  6  AgN08 

adding        6  Ag  +  8  HN03  ->  6  AgN03  +  4  H2O  +  2  NO 
or  3  Ag  +  4  HN03  -+  3  AgN03  +  2  H2O  +  NO 

6.  Zn  +  2  HN03  ->  Zn(N03)2  -f  2  H 

HN03  +  8  H  ->  3  H20  +  NH3 

NH3  +  HN03  ->•  NH4N03 

These  reactions  are  not  added  to  give  a  total  reaction,  because  they 
represent  only  a  part  of  the  reactions  that  are  taking  place,  and  the 
proportion  of  the  acid  which  acts  as  here  shown  varies  very  greatly 
according  to  conditions  of  temperature,  concentration,  and  amount 
of  resulting  product.  Hence  the  summation  of  these  three  equations 
could  not  be  used  to  calculate  the  amount  of  product  to  be  obtained 
from  a  given  weight  of  material.  Some  of  the  nitric  acid  will  be 
reduced  only  to  NO,  which  escapes  as  a  gas.  Possibly  some  N20 
and  free  N2,  and  probably  some  free  hydrogen  will  also  escape. 
Which  of  the  reaction  products  preponderates  in  a  given  case  de- 
pends, as  already  said,  on  the  conditions. 

7.  See  Section  396,  p.  371. 

8.  (NH4)2S04  +  Ca(OH)2  ->  CaS04+  2  NH3*+  2  H2O 

132.2  74.1 

132.2  :  74.1::  100  ix 

x  =  56.05  =  no.  of  grams  of  Ca(OH)2. 

9.  From  above  equation  it  is  seen  that  132.2  grams  of  (NH4)2S04 
yield  2  moles  or  2  X  22.4  liters  of  NH3. 

132.2:44.8::  100  :x 

x  =  33.9  =  no.  of  liters  of  NH3. 


100  COMPOUNDS  OF  NITROGEN 

10.   From  above  equation,  132.2  grams  of  (NH4)2S04  yield  2  X 
17.03  grams  of  NH3. 

132.2  :  34.06  :  :  100  :  x 
x  =  25.76. 


25.76  grams  of  pure  NH3  =     ~  =  92.0  grams  of  28%  solu- 

.60 

tion  of  NH3. 

no 

11.  92  grams  of  NH3  solution  of  sp.  gr.  0.90  occupy  -^  =  102.2 

U.  i7 

c.c. 

12.  3  Cu     +8  HN08  ->  3  Cu(NO3),  +  2  NO  +  4  H2O 
3  X  63.6      8  X  63 

190.8  :  504  :  :  190.8  :  x 
x  =  504. 

KftA 

504  grams  of  pure  HN03  =  ~  =  720  grains  of  70%  HN03. 

13.  From  above  equation,  190.8  grams  of  Cu  yield  2  X  22.4  liters 
=  44.8  liters  of  NO. 

14.  2  NO      +          02  ->  2  NO2 
44.8  1.  22.4  1. 

22  4 
22.4  liters  of  oxygen  =  -~  =112  liters  of  air. 

16.  The  reaction  of  the  explosion  of  gunpowder  is  expressed  ap- 
proximately by  the  equation  : 

2  KN03  +  3  C  +  S  -*  3  C02  +  N2  +  K2S. 
The  solid  K2S  is  responsible  for  the  smoke. 

Smokeless  powder  on  exploding  decomposes  according  to  the 
equation  : 

C12H1404(N03)6  ->  3  N2  +  7  H20  +  3  C02  +  9  CO 
which  shows  all  the  reaction  products  to  be  gaseous. 

16.  If  heat  is  given  off  when  N2O  decomposes  into  nitrogen  and 
oxygen,  this  heat  is  added  to  the  heat  of  combustion  of  a  substance 
burning  in  the  N20.  This  added  heat  would  compensate  partly  or 
wholly  for  the  heat  absorbed  by  the  inert  N2  produced  by  the  reac- 
tion. Thus  combustion  in  N20  may  be  practically  as  vigorous  as 
in  pure  oxygen. 


PAGES-377T39l  101 

CHAPTER   XXXI 

THE   HALOGEN   FAMILY;    THE   PERIODIC    SYSTEM 

Pages  377-391 

THE  alert  teacher  will  have  already  pointed  out  to  pupils  many 
family  resemblances  between  elements ;  as,  for  example,  the  chemical 
resemblance  between  oxygen  and  sulphur,  where  both  were  found 
to  unite  with  iron  in  some  of  the  earlier  experiments,  one  making 
the  oxide,  the  other  the  sulphide,  and  both  causing  the  release  of 
light  and  heat  when  the  reaction  was  rapid  enough.  Again,  when 
potassium  and  sodium  were  used  to  react  with  water,  family  resem- 
blance was  doubtless  pointed  out.  When  the  rare  gases  of  the  at- 
mosphere were  mentioned,  another  chance  to  point  out  the  close- 
ness of  relationship  in  a  natural  family  of  the  elements  occurred,  and 
this  time  chemical  inactivity  was  the  most  striking  resemblance. 

These  family  relationships  may  now  be  recalled  to  give  a  familiar 
setting  to  the  advance  work,  and  the  pupil's  knowledge  of  the  proper- 
ties of  chlorine  should  also  be  made  use  of  in  introducing  him  to  fluo- 
rine, bromine,  and  iodine. 

With  a  fairly  complete  knowledge  of  the  principal  resemblances 
between  the  four  members  of  the  halogen  family,  the  pupil  may  then 
be  given  some  account  of  the  marvelous  regularity  that  exists  among 
the  atomic  weights  of  the  elements,  and  its  relation  to  this  matter 
of  family  resemblances  may  be  shown. 

Pupils  will  always  be  found  to  be  much  interested  in  speculating 
as  to  what  is  back  of  this  wonderful  regularity ;  and  here  again,  as 
under  the  discussion  of  the  probable  atomic  structure  of  electricity 
(Section  331,  p.  314),  the  teacher  may  add  a  bit  of  the  more  recent 
theory,  and  briefly  explain  the  modern  conception  of  the  atom  as 
built  up  of  electrons.1 

Answers  to  Questions  on  Chapter  XXXI 
Page  391 

1.   The  halogens  resemble  each  other  in  that  they  all  possess  a 
most  disagreeable  odor ;  they  are  all  very  active  chemically,  com- 
1  See  Cox,  Beyond  the  Atom,  G.  P.  Putnam's  Sons. 


102      THE  HALOQEN  FAMILY?    THE  PERIODIC  SYSTEM 

bining  spontaneously  with  nearly  all  the  metals ;  and  their  hydrogen 
compounds  are  all  colorless  and  extremely  soluble  in  water,  in  which 
solution  they  become  strong  acids.  Their  valence  is  always  one 
towards  hydrogen  and  the  metals. 

2.  See  Section  403,  p.  379. 

3.  Fluorine  decomposes  water  instantly,  combining  with  the  hy- 
drogen and  driving  out  the  oxygen.     Mixed  with  hydrogen,  fluorine 
combines  explosively  even  in  the  dark. 

A  mixture  of  chlorine  and  hydrogen  does  not  combine  chemically 
if  it  is  kept  from  strong  light,  but  exposed  to  intense  light  or  touched 
with  a  flame  or  an  electric  spark  it  explodes  with  violence. 

Bromine  can  combine  directly  with  hydrogen,  but  not  with  vio- 
lence, if  a  mixture  of  the  two  is  passed  through  a  heated  tube. 

Iodine  combines  with  hydrogen  even  less  easily  than  does  bromine, 
although  the  compound  once  formed  remains  undecomposed  at  ordi- 
nary temperature. 

We  see  that  the  halogens  all  form  similar  compounds  with  hydro- 
gen, but  that  the  strength  of  the  attraction  decreases  regularly  in 
passing  from  the  halogen  of  lightest  atomic  weight  to  that  of 
heaviest  atomic  weight. 

4.  Free  iodine  gives  an  intense  blue  color  with  starch.     Combined 
iodine  does  not  give  this  color,  but  the  addition  of  a  little  chlorine 
will  liberate  the  iodine  from  combination  and  the  blue  color  with 
starch  will  appear. 

6.  To  demonstrate  the  presence  of  starch  in  a  sweet  potato, 
knead  a  little  of  the  cooked  potato  in  some  water  until  a  smooth 
thin  emulsion  is  obtained,  then  add  a  little  iodine  solution  and  note 
the  blue  color,  which  is  a  test  for  starch.  The  color  is  so  intense 
that  it  may  appear  black,  in  which  case  stir  a  little  of  the  emulsion 
into  a  large  volume  of  water. 

6.  See  Section  411,  p.  384. 

7.  A  glance  at  the  periodic  arrangement  of  the  elements  on  page 
389  shows  that  an  unknown  element  of  atomic  weight  about  99, 
and  another  of  atomic  weight  about  188  may  be  expected  to  exist 
and  to  fit  into  the  same  family  with  manganese;  that  two  with 
atomic  weights  between  208  and  222.4  may  be  expected  to  be  found 
and  to  fit  respectively  into  the  sulphur  and  halogen  families.     The 


PAGES  377-391  103 

properties  of  these  elements  will,  without  doubt,  prove  to  be  what 
would  be  expected  from  their  positions  in  their  respective  families. 

8.  K  =  39.1;  I  =  127;  KI  =  166. 

127 

In  1000  grams  of  KI  there  are  7  -  X  1000  =  765  grams  of 

loo 

iodine. 

9.  2KI  +     C12   ->2KC1  +I2 
332  g.       70.9  g. 

332  :  70.9  :  :  1000  :  x 

x  =213.6  grams  of  chlorine. 

10.  2  KI   +        Clf        -*2  KC1  +  I2 
332  g.         22.4  1. 

332  :  22.4  :  :  1000  :  x 

x  =  67.5  liters  of  chlorine. 

11.  At  100°  C.  the  molal  volume  is  2730l'Q100  x  22.4  =30.6  liters. 

Zio 

Therefore  30.6  liters  will  be  the  volume  occupied  by  1  mole,  or 
160  grams  of  Br2  vapor  at  atmospheric  pressure  and  100°  C. 
5c.c.  of  liquid  bromine  of  sp.  gr.  3.19  =  5  X  3.19  =  15.95 
grams.    As  a  gas  at  100°  C.,  this  will  occupy  a  volume  of 

X  3,0.6  =  3.05  liters. 


12.  (a)  CaF2  +  H2S04  ->  CaS04  +  2  HF  f 

(6)  Mn02  +  4  HBr  -+  MnBr2  +  2  H20  +  Bra 

(c)  Cu  +  Br2  ->  CuBr2 

(d)  CuO  +  2  HBr  ->  CuBr2  +  H20 

13.  (a)  2  K+  +  2  r  +  Cl,  -*  2  K+  +  2  Cl-  +  I2 

(6)  K+  +  Br-  +  Ag+  +  N03--^K++N03-+AgBr| 

(c)  Cu++  +  2  Br~  +  C12  ->  Cu++  +  2  Cl~  +  Br2 

(d)  2  H+  +  2  T  +  Zn  ->  Zn++  +  2  I~  +  H2| 

(e)  H+  -f  Br-  +  Na+  +  OH~  ->  Na+  +  Br  +  H20 
(/)  CuO  +  H20  ^±  Cu(OH)2  ^  Cu++  +  2  OR- 

2  Br  +  2  H+ 

2H20 

In  pure  water  the  horizontal  reaction  does  not  take  place  to  a 
perceptible  extent.     In  presence  of  HBr,  the  occurrence  of  the  ver- 


104  REVERSIBLE  CHEMICAL  REACTIONS 

tical  reaction  removes  very  completely  one  product  of  the  horizontal 
reaction,  and  thereby  the  latter  is  enabled  to  run  to  completion,  the 
copper  oxide  dissolving  and  ionized  copper  bromide  being  formed  in 
the  solution. 


CHAPTER  XXXII 

REVERSIBLE   CHEMICAL   REACTIONS;   CHEMICAL 
EQUILIBRIUM 

Pages  392-412 

As  was  the  case  with  the  study  of  the  periodic  law,  much  pre- 
liminary material  is  available  with  which  to  introduce  the  formal 
study  of  reversible  reactions  on  a  familiar  foundation. 

One  of  the  earliest  experiments  performed  by  most  classes  makes 
use  of  mercuric  oxide  in  obtaining  oxygen  by  heating  the  oxide. 
While  pupils  seldom  prepare  their  own  mercuric  oxide,  they  are 
always  made  familiar  with  the  fact  that  it  may  be  prepared  by 
merely  heating  mercury  in  air  or  in  oxygen,  and  they  themselves 
prepare  other  oxides  in  that  way. 

Thus,  while  the  matter  was  perhaps  not  called  to  their  attention 
at  that  time,  it  can  now  be  made  use  of  as  a  natural  lead  into  the 
new  topic  of  reversibility. 

Again,  the  fact  that  carbon  dioxide  reacts  feebly  with  water  to 
form  an  acid  was  early  learned  by  the  class  (Section  57,  p.  58),  and 
the  further  fact  that  the  carbonated  water  easily  reverted  to  water 
and  carbon  dioxide  was  pointed  out  in  connection  with  the  fire 
extinguisher  (Section  58,  p.  58).  This  can  now  be  recalled  as  an- 
other example  of  a  reversible  reaction. 

In  connection  with  the  study  of  crystal  hydrates  (Section  194,  p. 
185),  it  was  shown  that  some  substances  readily  react  with  water 
in  definite  proportion  to  form  new  products,  and  that  these  prod- 
ucts readily  decompose  on  slight  heating  and  yield  water  and  the 
original  anhydrous  substance. 

Again  (Section  219,  p.  208),  the  reaction  between  sulphur  dioxide 
and  water  was  specifically  shown  to  be  reversible  like  that  between 


PAGES  392^12  105 

carbon  dioxide  and  water.  Thus  there  are  many  foundations  on 
which  to  base  an  introduction  to  the  study  of  reversible  reactions. 
The  mass  law,  in  its  simple,  common  sense  form,  without  mathemat- 
ical complications,  can  readily  be  understood  by  pupils  of  high 
school  age,  and  its  use  explains  reactions  that  could  not  be  un- 
derstood without  it.  The  idea  of  chemical  equilibrium  is  a  valuable 
one  to  pupils  who  have  progressed  as  far  as  this  chapter. 

The  study  of  the  three  general  means  of  causing  reversible  re- 
actions to  proceed  to  completion  is  also  valuable. 

From  a  practical  standpoint,  the  study  of  hydrolysis  is  a  valuable 
application  of  the  principles  of  this  chapter.  The  extensive  use  of 
various  salts  such  as  sodium  carbonate,  borax,  sodium  phosphate 
(both  the  disodium  and  the  trisodium  salts),  soap,  and  alum  de- 
pends very  largely  on  their  hydrolysis,  and  their  action  cannot  be 
understood  without  reference  to  hydrolysis. 

Answers  to  Questions  on  Chapter  XXXII 

Page  412 

1.   Among  the  reversible  reactions  already  studied  are : 
(a)  2  HgO  ^±  2  Hg  +  0,.     Sections  21,  414,  pp.  29,  392. 
(6)  2  H2  +  02  ^±  2  H20.     Sections  119, 414,  pp.  117,  392. 

(c)  4  HC1  +  02  ^±  2  H20  +  2  C12.     Sections  170,  181,  pp.  165, 
171. 

(d)  2  NaHCOa  ^±  Na2C03  +  H2O  +  C02.     Section  192,  p.  183. 

(e)  CaC03  ^  CaO  +  C02.     Sections  207,  209,  pp.  195,  197. 
(/)  CaO  +  H20  ^±  Ca(OH)2.     Section  226,  p.  213. 

(g)  H2C03  +  CaC03  ^±  Ca(HC03)2.     Section  211,  p.  199. 

(h)  H2C03  ^  H20  +  C02.    Section  218,  p.  208. 

(i)   H2S03  ^±  H20  +  S02.     Section  219,  p.  208. 

(j)  NH3  +  H20  ^  NH4OH.     Sections  233,  391,  pp.  217,  368. 

(A;)  Fe203  +  3  CO  ^±  2  Fe  +  3  C02.     Section  256,  p.  244. 

(0   All  cases  of  ionization,  Chapter  XXV,  p.  299. 

(m)  H2  +  S  ^±  H2S.     Section  366,  p.  346. 

(n)  H2S  ^±  2  H+  +  S~.     Section  369,  p.  348. 


106  REVERSIBLE  CHEMICAL  REACTIONS 

(o)  2  BaO  +  02  ^±  2  Ba02.     Section  415,  p.  394. 
(p)  3  Fe  +  4  H20  ^±  Fe304  +  4  H2.     Section  417,  p.  396. 
(q)  2  NaCl  +  H2S04  ^t  Na2S04  +  2  HC1.     Section  420,  p.  400. 
(r)  Na2C03  +  H20  ^±  NaHC03  +  NaOH.     Sections  423,  424, 
pp.  403,  405. 

2.  Elevating  the  temperature  will  cause  many  reactions  to  run 
in  the  opposite  direction  to  that  followed  at  lower  temperature,  as 
for  example,  in  cases  a,  b,  d,  e,  f,  g,  h,  i,  j,  m,  and  o,  above. 

Changes  of  concentration  of  substances  entering  into  a  reaction 
from  one  side  or  the  other  may  cause  a  reaction  to  reverse,  or  to  go 
at  least  a  certain  distance  in  the  opposite  direction,  as,  for  example, 
in  cases  c,  h,  i,  j,  k,  I,  n,  p,  q,  r,  above. 

3.  See  Sections  416,  417,  pp.  395-398. 

4.  See  Sections  419,  420,  421,  pp.  399-401. 
6.   See  Section  424,  p.  405. 

6.  See  Section  424,  p.  405. 

7.  The  use  of  alum  in  baking  powders  depends  on  its  hydro- 
lyzing  and  yielding  an  acid.     The  use  of  sodium  carbonate  and  of 
borax  for  washing  depends  on  their  hydrolyzing  and  yielding  an 
alkali. 

8.  When  sodium  chloride  is  dissolved  in  water  its  molecules  begin 
to  dissociate  into  ions  at  a  very  rapid  rate,  and  all  would  shortly 
exist  in  the  ionized  state  except  that  Na+  and  Cl~  ions  in  solution 
are  continually  combining  to  form  undissociated  molecules.     The 
reaction  comes  to  equilibrium  when  as  many  molecules  are  being 
formed  in  a  given  interval  of  time  by  the  reuniting  of  ions  as  are 
dissociated  in  the  same  time.     The  condition  of  equilibrium  is 
reached  with  extreme  rapidity.     In  solutions  of  moderate  dilution 
about  80-90  per  cent  of  the  salt  is  ionized  at  this  point  of  equilib- 
rium. 

NaCl  ^±  Na+  +  Cl~ 

(o)  By  adding  a  solution  of  AgN03,  Cl~  ions  will  be  removed 
through  formation  of  the  insoluble  AgCl  precipitate.  This  removal 
of  Cl~  ions  will  displace  the  equilibrium  toward  the  right  until 
finally  all  of  the  NaCl  has  become  ionized. 

(b)  By  evaporating  the  water,  the  whole  concentration  is  in- 
creasing, but  that  of  both  the  Na+  and  Cl~  on  the  right-hand  side 


PAGES  413-424  107 

increasing  outweighs  the  increasing  of  only  the  NaCl  on  the  left- 
hand  side,  so  the  equilibrium  is  displaced  toward  the  left.  Soon, 
however,  the  concentration  of  the  NaCl  has  reached  its  saturation 
point  and  it  begins  to  crystallize,  or  precipitate,  out.  This  removal 
of  NaCl  still  further  displaces  the  equilibrium  toward  the  left,  and 
when  finally  the  water  has  all  been  evaporated,  the  reaction  has  gone 
completely  toward  the  left  and  only  undissociated  NaCl  is  left. 

9.  Guncotton  does  not  exist  in  a  state  of  chemical  equilibrium. 
It  has  an  extremely  strong  tendency  to  react  in  the  direction  of  the 
formation  of  simpler  compounds,  but  under  ordinary  conditions  the 
reaction  is  so  slow  that  it  is  negligible.  Once  provoke  the  reaction 
by  concussion  or  local  heating,  and  its  own  heat  so  hastens  the 
reaction  in  adjacent  portions,  that  the  whole  reaction  completes 
itself  in  a  brief  interval  of  time.  Thus  to  bring  guncotton  to  a  state 
of  equilibrium,  cause  it  to  explode,  whereupon  the  simpler  com- 
pounds are  formed  which  can  exist  together  in  a  true  state  of  equi- 
librium. The  reaction  is  Ci2H1404(N03)6  -V3  N2  +  7  H20  +  3C02 
+  9  CO.  This  is  not  a  reversible  reaction. 


CHAPTER   XXXIII 

CHEMICAL   REACTIONS  AND   ENERGY  TRANSFORMATIONS 

Pages  413-424 

IN  this,  the  final  chapter  of  Foundations  of  Chemistry,  an  attempt 
is  made  to  focus  attention  upon  the  energy  side  of  chemistry.  To 
be  sure,  the  pupil's  attention  has  many  times  been  called  to  the 
fact  that  energy  changes  always  accompany  chemical  changes,  but 
before  leaving  the  subject,  either  temporarily  or  permanently,  it  is 
well  for  the  pupil  to  be  reminded  that  chemistry,  like  physics,  is  con- 
cerned both  with  matter  and  with  energy,  and  that  although  most 
of  the  reactions  which  are  brought  about  by  mankind  in  the  affairs 
of  daily  life  and  in  the  laboratory  are  of  the  exothermic  type,  yet 
there  are  also  many  important  reactions  in  which  energy  is  absorbed. 
Most  important  of  these  are  those  changes  brought  about  in  green 
plants  under  the  influence  of  sunlight,  and  the  teacher  should  bring 


108  ENERGY  TRANSFORMATIONS 

in  here  the  botany  necessary  to  a  clear  explanation  of  such  part  of 
the  mechanism  of  photosynthesis  as  is  at  present  understood. 

Of  artificial  endothermic  reactions,  the  preparation  of  nitric  acid 
from  atmospheric  nitrogen  and  oxygen  is  perhaps  one  of  the  most 
important,  and  the  teacher  may  add  further  information  in  this 
regard.  (See  Knox,  The  Fixation  of  Atmospheric  Nitrogen,  D.  Van 
Nostrand  Co.) 

In  conclusion,  the  authors  would  make  a  final  appeal  to  teachers 
to  correlate  everywhere  what  is  being  taught  with  what  has  pre- 
ceded, and  also  with  the  daily  life  of  the  pupil.  Bring  in  and  use 
the  related  sciences  whenever  and  wherever  possible,  even  at  the 
risk  of  being  charged  with  teaching  general  science,  for  it  is  only 
by  teaching  science  as  a  whole,  and  not  as  consisting  of  isolated 
branches,  that  the  true  scientific  spirit  can  be  inculcated,  and  only 
thus  can  pupils  be  brought  to  realize  the  interrelation  of  all  the 
sciences  and  the  unity  of  nature. 

Answers  to  Questions  on  Chapter  XXXIII 
Page  424 

1.  Some  exothermic  reactions  which  are  used  solely  to  obtain 
heat  are :   (a)  The  burning  of  fuels,  Chapter  IV ;   (6)  The  thermit 
reaction,  Section  434,  p.  415 ;   (c)  The  burning  of  hydrogen  or  acety- 
lene in  the  oxyhydrogen  or  oxyacetylene  blowpipe,  Sections  118- 
119,  439,  pp.  116,  117,  420;    (d)  All  explosive  reactions,  since  the 
violent  expansion  is  caused  quite  as  much  by  the  enormous  heating 
of  the  gases  as  by  the  production  of  the  gaseous  substances  them- 
selves.    Except  for  the  use  of  the  gases  in  producing  the  expan- 
sion, the  material  products  of  explosions  are  entirely  waste. 

2.  Exothermic  processes  which  yield  energy  in  the  form  of  an 
electric  current  are  not  discussed  to  any  extent  from  this  point  of 
view  in  the  textbook.      Nevertheless,  information  given  in  Sec- 
tions 270,  342,  343,  346,  441,  pp.  257,  322,  323,  328,  423,  etc.,  has 
a  bearing  on  the  subject.     It  is  obvious  that  all  reactions  in  which 
the  number  of  electric  charges  on  the  ions  or  atoms  undergoes 
change   are  electro-chemical  reactions;    to   make  such   reactions 
develop  an  electric  current,  it  is  necessary  only  to  make  them  take 


PAGES  413^24  109 

place  in  suitable  cells.    For  example,  in  the  Daniell  cell  the  current 
is  produced  by  the  familiar  reaction, 

Zn  +  Cu++  +  S04"  ->  Zn++  +  S04~  +  Cu| 
If,  however,  a  strip  of  zinc  is  immersed  directly  hi  a  beaker  of 
copper  sulphate  solution,  the  zinc  is  dissolved  and  the  copper  is 
precipitated,  but  no  usable  current  is  obtained,  for  the  current 
simply  flows  through  the  metal  strip  from  where  the  Cu++  ions  are 
precipitated  to  where  the  Zn+4  ions  pass  into  the  solution.  But  in 
the  Daniell  cell,  the  zinc  strip  is  kept  physically  separated  from 
the  copper  sulphate  solution  by  means  of  a  porous  cup.  The  elec- 
tric charges  deposited  on  the  copper  strip  must  flow  as  a  current 
through  the  external  wire,  and  can  thus  be  made  to  ring  bells  or  do 
other  useful  work,  before  they  can  get  to  the  zinc  rod  to  enter  into 
the  formation  of  Zn++  ions.  This  is  the  secret  of  obtaining  an  elec- 
tric current  from  an  electro-chemical  reaction;  viz.,  to  keep  the 
reacting  substances  physically  separated,  so  that  the  interchange  of 
electric  charges  will  have  to  take  place  through  an  external  conductor. 
It  is  a  help  in  understanding  such  processes  to  consider  separately 
the  reactions  at  the  two  electrodes,  treating  the  ©  and  0  electrons  in 
the  same  way  as  material  atoms  in  writing  the  equations  (with  the 
exception  however  that  we  may  let  the  electrons  drop  out  of,  or 
appear  in,  the  equations  provided  only  that  the  number  of  ©  and 
0  that  appear  or  disappear  is  the  same).  For  example,  in  the 
Daniell  cell,  the  reaction  at  the  copper  electrode  is  : 
Cu++  +  S04"  ->  Cu°  +  SO"  +  2;© 
the  reaction  at  the  zinc  electrode  is: 


The  S04~~  ions  left  unbalanced  around  the  copper  electrode  have  to 
pass  through  the  wall  of  the  porous  cup  to  reach  the  locality  where 
they  can  electrically  balance  the  positive  Zn++  ions  being  formed. 

The  separate  reactions  in  the  lead  storage  cell  (Section  441,  p. 
423)  may  be  written  as  follows.  When  discharged,  both  plates  of 
the  battery  consist  of  PbS04.  The  electrolyte  is  moderately  con- 
centrated H2S04.  Charging,  at  +  electrode  : 

2  ©  +  PbS04  +  S04~  +  2  H2O  ->  PbO2  +  4  H+  +  2  SO4~ 
at  the  —  electrode  : 

20  +  PbS04  ->  Pb°  +  S04— 


110  ENERGY  TRANSFORMATIONS 

Adding  to  get  the  total  charging  reaction  : 

20  +  20  +  2  PbS04  +  2  H20  ->  Pb02  +  Pb°  +  4  H+  +  2  S04". 

Discharging,  at  the  Pb02  electrode  : 

Pb02  +  S04-  +  4  H+  ->  PbS04  +  2  H20  +  2  0 
at  the  Pb  electrode  : 

Pb°  +  S04~  ->  PbS04  +  20 
Adding  to  get  the  total  discharging  reaction : 

Pb°  +  Pb02  +  2  H2S04  ->  2  PbS04  +  2  H2O  +  20  +  20. 
In  the  Edison  storage  battery,  in  which  the  electrolyte  is  NaOH 
solution, 
Charging,  at  +  electrode : 

20+2  Ni(OH)2  +  2  OH-  ->  2  Ni(OH)3  -»  Ni,0,  +  3  H20 
at  the  -  electrode : 

20+  Fe(OH)2  ->  Fe°  +  2  OH~. 
Adding  to  get  total  charging  reaction : 

20  +  20  +  2  Ni(OH)2  +  Fe(OH)2  ->  Fe°  +  Ni203  +  3  H2O. 
Discharging,  at  Ni203  electrode : 

2  Ni(OH)3  ->  Ni(OH)2  +  2  OIT  +  2  © 
at  the  Fe  electrode: 

Fe°  +  2  OH-  ->  Fe(OH)2  +  20 
Adding  to  get  the  total  discharging  reaction : 

2  Ni(OH)3  +  Fe°  ->  2  Ni(OH)2  +  Fe(OH)2  +  20+20. 

3.  See  Section  437,  p.  418. 

4.  Two  common  explosives  in  which  the  power  is  developed  by 
the  decomposition  of  an  endothermic  substance  are  nitroglycerine 
and  guncotton.     Examples  of  other  endothermic  explosive  sub- 
stances, which  however  are  generally  not  used  intentionally  for 
such  a  purpose,  are  acetylene,  ozone,  and  hydrogen  peroxide. 

6.  Examples  of  explosive  mixtures  in  which  the  power  is  de- 
veloped through  the  formation  of  an  exothermic  compound,  are 
gunpowder,  the  oxyhydrogen  mixture,  the  hydrogen  chlorine  mix- 
ture, a  gasoline  vapor-air  mixture,  etc. 

6.  The  study  of  energy  is  usually  considered  as  belonging  to  the 
study  of  physics  rather  more  than  to  the  study  of  chemistry. 

Physics  deals  with  bodies  of  matter  rather  than  with  the  sub- 
stances of  which  the  matter  is  composed.  The  energy  of  motion 
of  a  body,  the  heat  energy  of  a  hot  body,  the  light  energy  emitted 


PAGES  413^24  111 

from  a  very  hot  body,  the  sound  energy  from  a  vibrating  body,  the 
transmission  of  mechanical  energy  by  a  belt,  of  electric  energy 
through  a  wire,  of  sound  energy  through  the  air,  all  come  within 
the  scope  of  physics,  as  they  are  concerned  only  with  bodies  of 
matter  and  do  not  involve  any  change  of  substance. 

But  chemical  changes  invariably  involve  the  giving  off  or  the 
absorption  of  heat  energy,  or  of  light  or  electrical  energy,  forms 
which  in  themselves  would  be  classed  as  physical  energy.  Since 
chemical  energy  is  thus  convertible  into  physical  as  well  as  physical 
into  chemical,  it  is  clear  that  the  sciences  of  physics  and  chemistry 
overlap. 

7.  Physiology  is  the  science  that  deals  with  the  vital  phenomena 
of  animals  and  plants.  Since  these  vital  phenomena  depend  on  the 
chemical  changes  taking  place  in  the  animal  and  plant  tissues,  or 
upon  the  energy  furnished  by  these  chemical  changes,  chemistry 
must  be  fundamental  to  an  understanding  of  physiology. 

Geology  treats  of  the  constitution  and  the  structure  of  the  earth 
and  of  the  history  of  the  development  of  the  structure.  The  con- 
stitution involves  a  knowledge  of  chemical  substances.  The  de- 
velopment of  the  structure  involves  chemical  changes  as  well  as 
physical.  For  example,  deposits  of  limestone  (Section  50,  p.  51), 
of  coal  (Section  277,  p.  266),  of  petroleum,  and  of  sulphur,  have 
very  clearly  resulted  from  chemical  reactions. 


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